All questions of Force and Energy for Primary 6 Exam

Gravitational Force

When a ball is thrown in the air upward, it eventually comes back down due to the gravitational force acting on it. This force is the attractive force between two masses, in this case, the ball and the Earth.

Explanation

- When the ball is thrown upwards, it moves against the force of gravity initially.
- However, as it reaches the peak of its trajectory, the gravitational force starts to pull it back towards the Earth.
- This force causes the ball to accelerate downwards until it eventually reaches the ground.

Impact of Gravitational Force

- The strength of the gravitational force depends on the mass of the two objects and the distance between them.
- In the case of the ball and the Earth, the Earth's mass is much greater, so the force of gravity pulls the ball towards it.
- This force is what causes objects to fall towards the Earth when they are not supported.

In conclusion, the reason why a ball thrown upwards eventually comes back down is due to the gravitational force between the ball and the Earth. This force causes the ball to accelerate downwards, following a path determined by the laws of physics.

Understanding Levers
A lever is a simple machine that helps us accomplish tasks with less effort. It consists of a rigid bar that pivots on a point called the fulcrum. Here’s how a lever makes work easier:
1. Reducing Effort
- Levers allow us to lift heavy objects with less force.
- By positioning the fulcrum closer to the load, you can lift the load with minimal effort.
2. Mechanical Advantage
- The lever provides mechanical advantage, meaning it multiplies the input force.
- For instance, using a long lever to lift a heavy rock allows a person to exert less force over a longer distance.
3. Increasing Efficiency
- Levers increase efficiency in completing tasks, making them quicker and less strenuous.
- This is particularly useful in tasks like lifting, pushing, or moving heavy items.
4. Practical Applications
- Everyday examples include seesaws, crowbars, and scissors, all of which utilize levers to simplify work.
- In construction, levers help move heavy materials, showcasing their importance in various fields.
Conclusion
In summary, levers are valuable tools that help us do work more efficiently by reducing the amount of effort needed. By understanding how they function, we can better appreciate their role in making our daily tasks easier.

Understanding Movement and Energy
To make things move, we need to use energy. Energy is the ability to do work, and it comes in various forms. Let's explore why energy is the correct answer and how it relates to movement.
Types of Energy
- Kinetic Energy: This is the energy of motion. When an object is moving, it possesses kinetic energy. For example, a rolling ball or a running person has kinetic energy.
- Potential Energy: This is stored energy that has the potential to cause movement. For instance, a drawn bow or a raised weight has potential energy, which can be transformed into kinetic energy when released.
Energy and Movement
- Energy Transfer: For an object to move, energy must be transferred to it. This can happen through various means, such as pushing, pulling, or even using engines.
- Muscular Force: While muscular force (option b) is a way to exert energy, it is not the only method. Energy can also come from mechanical, electrical, or chemical sources.
- Gravitational Force: This is a specific type of force that can assist in movement, but it does not directly cause things to move unless energy is applied.
- Friction: Although friction can affect movement by slowing things down, it is not a source of energy. Instead, it is a force that opposes motion.
Conclusion
In summary, energy is the fundamental requirement for making things move. Whether through kinetic or potential energy, it enables objects to shift from one place to another. Understanding energy is key to grasping how movement occurs in our world.

Understanding Simple Machines
A simple machine is a device that can change the direction or magnitude of a force. One common type of simple machine is the inclined plane.
What is an Inclined Plane?
An inclined plane is a flat surface that is tilted at an angle to the horizontal. It allows objects to be moved from a lower height to a higher height with less effort.
Characteristics of an Inclined Plane:
- Slope Structure:
It has one end that is higher than the other, creating a slope. This design makes it easier to lift heavy objects.
- Force Distribution:
Instead of lifting an object vertically, which requires more force, the inclined plane allows the force to be applied over a longer distance at a gentler angle.
Real-World Examples:
- Ramps:
Used for wheelchair access or loading goods onto trucks.
- Slides:
Playground slides are also a form of inclined planes that provide fun while demonstrating the concept.
Benefits of Using an Inclined Plane:
- Reduced Effort:
It decreases the amount of force needed to lift an object.
- Safety:
Moving heavy items becomes safer and easier, reducing the risk of injury.
In conclusion, an inclined plane is a fundamental simple machine that utilizes a slope to make lifting and moving objects more efficient. This design illustrates the principles of physics by leveraging gravity and force.

Understanding the Components of a Pulley
A pulley is a simple machine that helps in lifting heavy objects with ease. The main components of a pulley include:
1. Ropes
- Ropes are critical for the functioning of a pulley. They are used to connect the load that needs to be lifted to the pulley system.
- When you pull down on one end of the rope, it creates an upward force on the other end, allowing you to lift the load.
2. Grooved Wheel
- The grooved wheel is the circular component that the rope runs over.
- Its groove helps to keep the rope in place while allowing it to move smoothly.
- This wheel significantly reduces friction, making it easier to lift heavy loads.
3. Supporting Structure
- While not always mentioned as a primary component, the structure that holds the pulley in place is essential.
- This can be a fixed beam, a hook, or any sturdy support that allows the pulley to function effectively.
Why Other Options are Incorrect
- A Lever: This is a different type of simple machine that works on the principle of balance and force but is not a component of a pulley.
- A Beam Balance: This is used for measuring weight and does not relate to the function of a pulley.
- A Thermometer: This device measures temperature and has no connection to the mechanics of a pulley.
In summary, the major components of a pulley are the ropes and the grooved wheel, making option 'A' the correct answer. Understanding these components helps in appreciating how pulleys make lifting tasks easier and more efficient.

**Friction opposing the box**

Friction is a force that opposes the motion of objects when they are in contact with each other. It acts in the opposite direction to the applied force, making it more difficult for objects to move. In this case, when loading boxes onto a truck using a ramp, friction plays a crucial role in making the process smoother.

**The role of friction in loading boxes on a truck ramp:**

1. **Preventing the box from slipping:** When a box is placed on a ramp, gravity tries to pull it downward. Without friction, the box would simply slide down the ramp, making it difficult to load onto the truck. However, friction between the box and the ramp's surface provides the necessary grip to prevent the box from slipping.

2. **Helping to control the speed of the box:** Friction also helps to control the speed at which the box moves down the ramp. If there was no friction, the box would slide down the ramp very quickly, potentially causing it to collide with other boxes or objects on the truck. Friction slows down the box's motion, allowing for better control during the loading process.

3. **Reducing the force required to push the box:** When friction is present, the force required to push the box up the ramp is reduced. Friction acts in the opposite direction to the applied force, making it easier to move the box. Without friction, the person loading the boxes would have to exert a much greater force to overcome the lack of grip between the box and the ramp.

4. **Preventing damage to the box:** Friction helps to keep the box stable and prevents it from sliding or toppling over during the loading process. This helps to minimize the risk of damage to the box and its contents.

In conclusion, friction is essential in making the loading of boxes onto a truck ramp smoother. It prevents the box from slipping, helps to control its speed, reduces the force required to push the box, and prevents damage to the box. Therefore, the correct answer is option 'C' - friction opposing the box.

Muscular force is applied when we push or pull something using our muscles. A boy pushing a bicycle is an example of muscular force.

Ensuring the moving parts of machines are well lubricated helps prevent accidents and ensures smooth operation. Additionally, sharp tools should be handled with care and stored properly.

The sun is not a direct source of electrical energy, though it is a source of solar energy. Electrical appliances like fans, washing machines, and computers use electrical energy generated at power stations and supplied to our homes through wires.