# Forces: Primary 6 Science Topic (PSLE SEAB Syllabus) Free Online Lessons

### What is a force?

A force is a push or a pull that can make an object move, stop, or change direction. A force cannot be seen but its effects after can be felt and seen (destruction, change in shape, speed or direction). There are many types of forces, including gravity, friction, air resistance, and magnetism. Here are the PSLE Science forces notes.

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Gravity is the force that pulls objects towards each other, such as the force that pulls an apple towards the ground. Friction is the force that resists motion between two surfaces that are in contact, such as the force that slows down a moving toy car on a carpet.

Air resistance is the force that acts against the motion of an object through the air, such as the force that slows down a falling feather. Magnetism is the force that attracts or repels objects that have magnetic properties, such as the force between a magnet and a metal object.

Forces can be measured in units called Newtons (N), and the direction of a force can be represented by arrows. Understanding the concept of forces is important in explaining how things move and interact with each other in our world. Here are the PSLE Science forces notes.

### A force occurs in pairs. Push or Pull.

A force is a push or a pull that can make an object move, stop, or change direction. To understand how a force can be a push or a pull, it is helpful to think about some examples.

Push

• pressing
• stepping
• squeezing
• pushing

Pull

• Tugging
• Dragging
• Stretching
• Pulling

Other types of forces (Torque)

• Turning
• Twisting
• Wringing

When you push a toy car, you are applying a force to it. Your push causes the car to move forward, so in this case, the force is a push. On the other hand, if you pull a wagon behind you, the force is a pull. Your pull causes the wagon to move towards you, which is the opposite direction of the force.

In both cases, a force is being applied to an object, and the direction of the force determines whether it is a push or a pull. Another example is when you throw a ball. When you release the ball, you are applying a force to it in the direction of the throw, which is a push. The ball then moves through the air due to the force you applied.

To summarise, a force can be a push or a pull, and the direction of the force depends on the direction of the movement it causes. A force can make an object move, stop, or change direction, and understanding the concept of forces is important in explaining how things move and interact with each other in our world.

### PSLE Science for Primary Schools

The syllabus requirements for the topic of Forces in primary schools in Singapore, as set by the Ministry of Education (MOE) and administered by the Singapore Examinations and Assessment Board (SEAB), are as follows:

1. Students should be able to define a force as a push or a pull that can make an object move, stop, or change direction.
2. Students should be able to identify different types of forces, including gravity, friction, air resistance, and magnetism.
3. Students should be able to explain how forces can affect the motion of an object and how the amount of force applied affects the speed and direction of the object’s movement.
4. Students should be able to measure forces using appropriate instruments and units, such as the spring balance and Newtons (N).
5. Students should be able to identify the different factors that affect the strength and direction of a force, such as the distance between objects, the mass of the objects, and the type of surfaces in contact.
6. Students should be able to apply their understanding of forces to real-life situations, such as the motion of toys, vehicles, and sports equipment.

The primary school syllabus on forces aims to help students develop a foundational understanding of the concept of forces, their effects, and how they can be measured and applied in real-world situations.

### Newton’s Laws of Motion

1. Newton’s first law of motion: An object at rest stays at rest, and an object in motion stays in motion with a constant velocity, unless acted upon by an unbalanced force. This means that an object will continue to do what it is doing (either stay still or keep moving) unless something else makes it change. For example, a ball will stay still on the ground until someone kicks it, or a rolling ball will keep moving until it hits something and stops.
2. Newton’s second law of motion: The acceleration of an object is directly proportional to the force applied, and inversely proportional to the mass of the object. This means that the more force you apply to an object, the more it will accelerate, and the more massive the object, the harder it is to accelerate. For example, a small ball will accelerate faster than a large ball if you apply the same amount of force to both.
3. Newton’s third law of motion: For every action, there is an equal and opposite reaction. This means that when two objects interact, they exert equal and opposite forces on each other. For example, if you push against a wall, the wall is also pushing back on you with an equal force.

### Balanced Forces

A balanced force is a situation where two or more forces acting on an object are equal in size and opposite in direction, causing the object to remain stationary or to move with a constant velocity. In other words, the net force acting on the object is zero.

When there is a balanced force, the object is not accelerating, which means its speed and direction are not changing. This can be seen in a variety of everyday situations, such as when you push a chair with the same force as someone else pulling it, the chair will not move because the forces are balanced.

Here are three examples of balanced forces:

1. Tug-of-War: In a game of tug-of-war, two teams pull on a rope in opposite directions with the same force. If both teams are equally matched, the forces will be balanced, and the rope will remain in the same place without moving.
2. Object at rest: When an object is sitting still on a surface, there are two balanced forces acting on it. Gravity pulls the object downward, and the normal force of the surface (such as a table or the ground) pushes up on the object with the same amount of force. Because the two forces are equal and opposite, the object stays in place.
3. Object moving at a constant speed: When an object is moving at a constant speed in a straight line, the forces acting on it are balanced. For example, a car driving on a straight, level road at a constant speed experiences a balanced force. The force of the engine moving the car forward is balanced by the force of air resistance and friction from the road pushing back on the car. The balanced forces keep the car moving at a constant speed without accelerating.

To summarise, balanced forces occur when two or more forces acting on an object are equal in size and opposite in direction, causing the object to remain stationary or to move with a constant velocity.

### Unbalanced Forces

An unbalanced force is a situation where two or more forces acting on an object are not equal in size or direction, causing the object to accelerate, change direction, or stop moving altogether. In other words, the net force acting on the object is not zero.

When there is an unbalanced force, the object is accelerating in the direction of the larger force. This can be seen in a variety of everyday situations, such as when you kick a soccer ball, the force of your foot pushing on the ball is greater than any friction or air resistance acting on the ball, causing it to accelerate in the direction of your kick.

Here are three examples of unbalanced forces:

1. Kicking a ball: When you kick a ball, you are applying a force to it that is greater than any forces acting against it, such as air resistance or friction. The ball accelerates in the direction of the kick, because the net force is no longer zero.
2. Riding a bike up a hill: When you ride a bike up a hill, you are working against gravity, which is pulling you and the bike downwards. To keep moving forward, you need to pedal with a force that is greater than the force of gravity pulling you down. The resulting unbalanced force causes you and the bike to accelerate forward and upward.
3. Car braking: When a car brakes, the friction between the brake pads and the wheels causes an unbalanced force that slows down the car. The force of the brakes pushing against the wheels is greater than the force of the wheels pushing the car forward, causing the car to decelerate and eventually stop.

Unbalanced forces occur when two or more forces acting on an object are not equal in size or direction, causing the object to accelerate, change direction, or stop moving altogether. These forces are important in understanding how objects move and how they interact with their environment.

### How does a force affect an object

A force affects an object in several ways:

1. Change in motion: A force can cause an object to start moving or to stop moving. If an object is at rest and a force is applied, the object will start moving. If an object is already moving, a force can cause the object to stop or change direction.
2. Change in speed: A force can also cause an object to speed up or slow down. For example, if a force is applied to a moving object in the same direction as its motion, it will speed up. On the other hand, if a force is applied in the opposite direction to its motion, it will slow down.
3. Change in shape: A force can also change the shape of an object. For example, if you squeeze a ball, you are applying a force that changes its shape. Similarly, if you pull a rubber band, you are applying a force that stretches it.
4. Change in direction: A force can change the direction of an object’s motion. For example, when you hit a tennis ball with a racket, you are applying a force that changes the direction of the ball’s motion.

### Contact Forces

Contact forces are forces that require physical contact between two objects for them to occur. These forces arise from the interaction between the two objects when they come in contact with each other. There are different types of contact forces, including friction, tension, and normal force. Here are some simple explanations of these contact forces for primary school students:

1. Friction: Friction is a force that opposes motion between two objects that are in contact with each other. For example, when you try to slide a book across a table, the friction between the book and the table prevents it from moving easily. The amount of friction depends on factors such as the roughness of the surfaces in contact and the force pushing the objects together.
2. Tension: Tension is a force that occurs in a stretched or compressed object. For example, when you pull on a rubber band, you are applying a force that creates tension within the rubber band. The greater the force, the greater the tension, and the more the rubber band stretches.
3. Normal force: Normal force is a force that acts perpendicular to the surface of an object that is in contact with another object. For example, when a book rests on a table, the table exerts an upward normal force on the book to support its weight. The normal force is equal and opposite to the weight of the object, which is the force of gravity pulling the object downwards.

### Non-contact forces

Non-contact forces are forces that act on an object without any physical contact between the object and the force source. These forces can act at a distance, and they include forces such as gravity, magnetic forces, and electric forces. Here are some simple explanations of these non-contact forces for primary school students:

1. Gravity: Gravity is a force that pulls all objects towards each other. For example, the gravity of the Earth pulls objects towards its center, which is why things fall down when we drop them. The strength of gravity depends on the mass of the objects and the distance between them.
2. Magnetic forces: Magnetic forces are forces that act between objects with magnetic properties. For example, when you hold a magnet near a metal object, the magnet exerts a magnetic force on the metal object. The force can either attract the metal object towards the magnet or repel it away from the magnet, depending on the poles of the magnets.
3. Electric forces: Electric forces are forces that act between charged objects. For example, when two balloons are rubbed against a woolen cloth and then brought near each other, they can either attract or repel each other, depending on their charge.

### Drawing Force diagrams

In primary school, students learn to draw force diagrams as a way to represent and visualize the forces acting on an object. Force diagrams are simplified diagrams that show the different forces acting on an object and the direction in which those forces are acting.

There are several reasons why force diagrams are useful in primary school:

1. Understanding how forces affect motion: Force diagrams help students to understand how different forces can affect the motion of an object. By drawing a diagram, students can see the direction and size of the forces, which can help them understand how the forces are acting on the object and how they are affecting its movement.
2. Identifying balanced and unbalanced forces: Force diagrams help students to identify whether the forces acting on an object are balanced or unbalanced. By comparing the size and direction of the different forces, students can determine whether the object is moving, accelerating, or remaining stationary.
3. Developing critical thinking skills: Drawing force diagrams requires students to use critical thinking skills, such as analyzing and interpreting information, making connections between different concepts, and problem-solving.
4. Supporting scientific inquiry: Drawing force diagrams supports scientific inquiry by helping students to develop a better understanding of how scientific concepts, such as forces, work in the real world. By visually representing the forces acting on an object, students can better understand the cause-and-effect relationship between forces and motion.

### Types of Forces

There are several different types of forces that exist in the physical world. Some of the major types of forces include:

1. Contact forces: These are forces that require physical contact between two objects to occur, such as friction, tension, and normal force.
2. Non-contact forces: These are forces that act on an object without any physical contact between the object and the force source, such as gravity, magnetic forces, and electric forces.
3. Applied forces: These are forces that are applied to an object by another object or by a person, such as pushing, pulling, or twisting.
4. Elastic spring forces: These are forces that occur when a spring is stretched or compressed. The force depends on the spring constant, which is a measure of how stiff the spring is.
5. Buoyant forces: These are forces that occur when an object is immersed in a fluid. The force is directed upwards and is equal to the weight of the fluid displaced by an object.
6. Frictional forces: These are forces that oppose motion and act in the opposite direction of the applied force. They occur when two surfaces rub against each other and can be influenced by factors such as surface roughness and the force pushing the objects together.
7. Magnetic forces: These are forces that act between objects with magnetic properties, such as two magnets. They can either attract or repel each other, depending on the poles of the magnets.
8. Electric forces: These are forces that act between charged objects. Like magnetic forces, they can either attract or repel each other, depending on their charges.
9. Tension forces: These are forces that occur in a stretched or compressed object, such as a rope or wire. The force is directed along the length of the object and depends on the magnitude of the stretching or compression.

### Friction

Friction is a force that opposes motion and acts in the opposite direction of the applied force. In other words, it is the force that makes it difficult for objects to move past each other when they are in contact. For example, when you try to slide a book across a table, the friction between the book and the table prevents it from moving easily. Friction is caused by the irregularities on the surfaces of the objects in contact.

There are two types of friction: static friction and kinetic friction.

1. Static friction is the friction that exists between two objects that are not moving relative to each other. For example, when you try to push a heavy box across the floor, there is a static friction force that opposes the force you are applying. Once the force you are applying is greater than the maximum static friction force, the object will start to move.
2. Kinetic friction is the friction that exists between two objects that are moving relative to each other. For example, when you push a box across the floor, there is a kinetic friction force that opposes the direction of motion.

The amount of friction depends on factors such as the roughness of the surfaces in contact and the force pushing the objects together. For example, smoother surfaces have less friction than rough surfaces, and heavier objects have more friction than lighter objects.

Friction can be both helpful and harmful. On the one hand, it helps us walk without slipping and allows us to write on paper. On the other hand, it can cause wear and tear on machines and cause energy to be lost as heat.

### What causes friction?

Friction is caused by the interaction between two surfaces that are in contact with each other. Even surfaces that appear to be very smooth actually have tiny bumps and roughness on them when viewed under a microscope. When these surfaces are pressed together and moved against each other, these tiny bumps and roughness interact and create resistance to motion.

The amount of friction between two surfaces depends on several factors, including the roughness of the surfaces, the force pressing the surfaces together, and the materials of the surfaces. Rough surfaces create more friction than smooth surfaces, while heavy objects create more friction than light objects. The type of materials also affects friction – for example, rubber has higher friction than ice, which is why it is easier to walk on dry ground than on ice.

Friction can have both positive and negative effects, depending on the situation.

Positive effects of friction include:

1. Providing traction: Friction between our feet and the ground allows us to walk, run, and climb without slipping.
2. Generating heat: Friction can generate heat, such as when we rub our hands together on a cold day.
3. Preventing slippage: Friction can prevent objects from slipping or sliding too much, which is important in applications such as braking and tires.

Negative effects of friction include:

1. Wearing down surfaces: Friction can cause materials to wear down over time, such as the soles of our shoes or the brake pads on a car.
2. Reducing efficiency: Friction can reduce the efficiency of machines and devices by converting some of the energy into heat. For example, friction in engines and transmissions can reduce fuel efficiency.
3. Causing damage: Friction can cause damage to materials or surfaces that are in contact with each other, such as scratches or dents.

### How to reduce friction to our advantage

There are several ways to reduce friction forces between two surfaces, including:

1. Lubrication: Adding a lubricant, such as oil, grease, or wax, between the two surfaces can reduce friction by allowing them to slide more easily against each other.
2. Smoothing the surfaces: Reducing the roughness of the surfaces that are in contact with each other can reduce friction. This can be done by polishing, grinding, or coating the surfaces.
3. Using ball bearings or rollers: By placing ball bearings or rollers between two surfaces, friction can be reduced, as the ball bearings or rollers roll instead of sliding, reducing the contact area and the amount of friction.
4. Reducing the force pressing the surfaces together: By reducing the force that is pressing the two surfaces together, the amount of friction can be reduced. This can be done by using lighter materials or reducing the load on the surfaces.
5. Using non-stick coatings: Applying non-stick coatings, such as Teflon, to one or both surfaces can reduce friction by reducing the amount of contact between the surfaces.
6. Streamlining aerodynamics: Air resistance can create a significant amount of drag, which can increase the amount of friction that a moving object experiences. By reducing drag, the amount of friction can be reduced, allowing the object to move more easily.

Reducing friction is important in many applications, such as in the design of machinery, transportation systems, and medical devices.

Here are some reasons why we reduce friction:

1. To improve efficiency: Reducing friction can improve the efficiency of machines and devices by reducing the amount of energy that is lost to friction. For example, a well-lubricated engine will run more smoothly and require less fuel than one with high friction.
2. To reduce wear and tear: Friction can cause materials to wear down over time, which can lead to damage and reduce the lifespan of machines and devices. By reducing friction, we can reduce the amount of wear and tear, increasing the lifespan of the machine.
3. To improve safety: Reducing friction can improve safety in many applications, such as in transportation systems. By reducing friction between moving parts, we can reduce the risk of accidents and improve overall safety.
4. To increase speed: Friction can reduce the speed of machines and devices by creating resistance to motion. By reducing friction, we can increase the speed of the machine, improving performance in applications such as transportation, manufacturing, and automation.
5. To lower noise produced: Friction can produce a lot of noise when machines are working. With better lubrication, these annoying noises can be lowered or eliminated. It is a part of NVH controls for a better environment.

### Gravitational force

Gravitational force is the force that pulls all objects with mass towards each other. This force is what causes objects to fall to the ground when we drop them, and it is also what keeps the planets in orbit around the sun.

For primary school students, it can be explained as follows: every object in the universe has a force that pulls other objects towards it. The strength of this force depends on the mass of the object and the distance between the objects. The greater the mass of an object, the greater the gravitational force it exerts, and the closer two objects are to each other, the greater the gravitational force between them.

The force of gravity is always directed towards the center of an object. For example, the force of gravity on Earth is directed towards its center, which is why objects fall towards the ground. The force of gravity between two objects decreases as the distance between them increases. This is why objects appear to weigh less on the moon than they do on Earth, because the moon has less mass than Earth and is farther away from the center of the Earth.

### Magnetic Forces

Magnetic force is a force that occurs between objects with magnetic properties, such as two magnets. These objects can either attract or repel each other, depending on the poles of the magnets. The force is strongest at the poles of the magnets, where the magnetic field is strongest.

For primary school students, it can be explained that magnets have north and south poles, and opposite poles attract while like poles repel. For example, when you hold two magnets close together, the north pole of one magnet will attract the south pole of the other magnet, while the north pole of one magnet will repel the north pole of the other magnet.

The strength of the magnetic force depends on the distance between the magnets and the strength of their magnetic fields. The magnetic field is the area around a magnet where the magnetic force is felt.

Magnetic force is important in everyday life because it is used in many devices, such as motors, generators, and compasses. Magnets are also used in various industries, such as medicine, transportation, and electronics.

### Torque

Twisting Force. Torque is a force that causes an object to rotate around an axis or pivot point. It is also sometimes called a moment or a turning force. Torque is a vector quantity, which means it has both magnitude and direction.

For primary school students, it can be explained that torque is like a twisting force that can make an object spin. For example, when you turn a doorknob, you are applying a torque force that causes the door to rotate around its hinges.

The amount of torque depends on the magnitude of the force and the distance between the force and the axis of rotation. The greater the force or the farther the force is from the axis of rotation, the greater the torque. This means that a small force applied at a great distance from the axis of rotation can create the same amount of torque as a large force applied close to the axis.

Torque is important in many everyday applications, such as opening doors, turning screws, and riding a bicycle. It is also important in many industries, such as manufacturing and engineering.

### Elastic Spring Force

Elastic spring force is the force that is exerted by an elastic material, such as a spring, when it is stretched or compressed. When a spring is stretched or compressed, it stores potential energy, which can be released as kinetic energy when the spring returns to its original shape.

For primary school students, it can be explained that when a spring is stretched or compressed, it wants to return to its original shape, and the force that the spring exerts to resist the stretch or compression is the elastic spring force. This force is proportional to the amount that the spring is stretched or compressed. The greater the stretch or compression, the greater the force.

The amount of elastic spring force can be calculated using Hooke’s law, which states that the force exerted by a spring is equal to the spring constant multiplied by the amount of stretch or compression. The spring constant is a measure of how stiff the spring is, and it varies depending on the material and the size and shape of the spring.

Elastic spring force is important in many everyday applications, such as in shock absorbers, springs in mattresses and couches, and in many mechanical systems that require energy to be stored and released.

### Buoyancy Forces

Buoyant force is the upward force exerted on an object when it is immersed in a fluid, such as water or air. This force is caused by the pressure difference between the top and bottom of the object.

For primary school students, it can be explained that when an object is placed in a fluid, such as a ball in a pool, it displaces an amount of fluid that is equal to its own volume. The displaced fluid exerts an upward force on the object, which is the buoyant force. The buoyant force is equal to the weight of the fluid that is displaced by the object.

The buoyant force is what makes some objects float in a fluid, such as a boat in water. If the buoyant force is greater than the weight of the object, the object will float. If the weight of the object is greater than the buoyant force, the object will sink.

The buoyant force is affected by factors such as the density of the fluid and the volume and shape of the object. Objects that are less dense than the fluid will experience a greater buoyant force and are more likely to float.

Buoyant force is important in many everyday applications, such as in swimming, boat design, and deep sea diving. It is also important in scientific research, such as the study of ocean currents and the behavior of marine animals.

Archimedes’ principle is a scientific law that states that the buoyant force exerted on an object immersed in a fluid is equal to the weight of the fluid that the object displaces. This means that an object will float in a fluid if it displaces a volume of fluid that weighs more than the object itself. It was discovered by the ancient Greek mathematician and inventor Archimedes, and it is used in many fields of science and engineering, such as ship design and fluid mechanics.

### Molecular forces

Molecular forces are the attractive or repulsive forces that exist between molecules in a substance. These forces play a key role in determining the physical properties of a substance, such as its melting and boiling points, viscosity, and solubility. There are several types of molecular forces, including dipole-dipole forces, hydrogen bonding, and London dispersion forces. Understanding molecular forces is important in many fields of science, including chemistry, physics, and materials science, and helps to explain the behavior of substances.

### Pressure Force

Pressure force is the force exerted on a surface due to the pressure of a fluid or gas. It is calculated as the force per unit area and is measured in units such as Pascals or pounds per square inch. Pressure force is important in many fields of science and engineering, including fluid mechanics, aerodynamics, and materials science. It helps to explain phenomena such as buoyancy, lift, and drag, and is used in many applications, such as in hydraulic systems, pneumatic systems, and aircraft design.

### Fluid Friction

Fluid friction, also known as viscous drag, is the frictional force that exists between a fluid, such as air or water, and an object that is moving through it.

Fluid friction occurs because the fluid molecules near the surface of the object are slowed down due to the contact with the object. This causes a layer of slower-moving fluid, known as the boundary layer, to form around the object. The boundary layer increases the amount of friction that the object experiences and can cause it to slow down or become unstable.

The amount of fluid friction that an object experiences depends on several factors, including the shape and size of the object, the speed of the object, and the properties of the fluid. Streamlined objects, such as airplane wings, are designed to minimize fluid friction and create lift instead.

### Parachute

Here is a step-by-step summary of how a parachute works using forces and friction:

1. A person wearing a parachute jumps out of an airplane, starting to fall towards the ground due to gravity.
2. As the person falls, the air resistance against their body increases, which creates frictional forces between their clothing and skin and the air molecules.
3. When the parachute is opened, it creates a large surface area that catches the air flowing over the canopy.
4. The air flowing over the surface of the canopy creates a drag force, which acts against the downward force of gravity.
5. The combination of air resistance and drag force slows down the person’s descent, reducing their acceleration towards the ground.
6. The frictional forces between the air molecules and the person’s body and clothing help to slow down the descent even further.
7. The person wearing the parachute lands safely on the ground, having used the combined forces of air resistance and friction to slow their descent.

Experiment reducing friction

### What is NVH?

NVH stands for Noise, Vibration, and Harshness. It is a term used to describe the unwanted sounds and vibrations that are produced by machines and devices. These unwanted sounds and vibrations can have a negative impact on human health and well-being.

Noise can cause hearing damage, tinnitus, and other health problems. Exposure to loud noise can also cause stress, anxiety, and sleep disturbance. Long-term exposure to noise can increase the risk of cardiovascular disease, hypertension, and other health problems.

Vibration can also have negative effects on human health, such as causing musculoskeletal disorders, such as carpal tunnel syndrome or back pain. Prolonged exposure to vibrations can cause neurological disorders, such as numbness and tingling in the fingers, and can increase the risk of back injuries.

Harshness refers to the uncomfortable or jarring sensations that can be caused by vibrations or sounds. This can cause discomfort and stress, which can lead to fatigue, headaches, and other health problems.

Overall, reducing NVH is important for protecting human health and well-being. By designing machines and devices to produce less noise, vibration, and harshness, we can create a safer and more comfortable environment for people to live and work in.