Class 8 Science - Force and Pressure CBSE Worksheets Solutions

Q.1. Give one practical application of magnetic force. 

The closing mechanism of a refrigerator door is a practical example of magnetic force. It works as follows:

• The door has a magnetic strip that aligns with a metal frame.
• When the door is closed, the magnets attract each other, keeping the door securely shut.
• This prevents cold air from escaping, maintaining the internal temperature.

Q.2. Explain why snowshoes stop you from sinking into the snow. 

Snowshoes prevent you from sinking into the snow by using their design effectively:

• They have large, flat soles that distribute weight over a wider area.
• This design reduces the pressure exerted on the soft snow.
• As a result, wearers can walk on the surface without sinking.

Q.3. Which force can be used to gather iron pins scattered on the floor? 

Magnetic force can be used to gather iron pins scattered on the floor.

Q.4. Write one example where force changes the speed of a moving object.

The speed of a moving rubber tyre or a ring increases when it is pushed. This is because the applied force causes the object to accelerate.

Q.5. What is meant by a non-contact force? Give an example.

A non-contact force is a type of force that can act on an object without any physical contact. Key points include:

• It can exert its influence from a distance.
• For example, the force exerted by a magnet on another magnet is a non-contact force.

Other examples include:

• Gravitational force, which pulls objects towards the Earth.
• Electrostatic force, which can attract or repel charged objects.

Q.6. What is meant by atmospheric pressure? 

The atmospheric pressure is the weight of the air above us, extending many kilometres into the atmosphere. It is defined as:

• The force exerted by the air on a unit area.
• It can be imagined as the weight of a long column of air pressing down on a surface.
• This pressure is significant; for instance, it can be compared to the weight of a 225 kg object on a small area of 15 cm x 15 cm.

When we press a rubber sucker against a surface, it sticks because the air pressure outside is greater than the pressure inside the sucker, demonstrating the strength of atmospheric pressure.

Q.7. Why do the shape and size of balloons change when filled with air or water? 

The shape and size of balloons change when filled with air or water due to the pressure exerted by the molecules inside. This process can be explained as follows:

• When air or water fills a balloon, the molecules move rapidly and collide with the walls.
• These collisions create a high pressure that pushes against the balloon's surface.
• As a result, the balloon expands and inflates, altering its shape and size.

In summary, the expansion of a balloon is a direct result of the pressure from the gas or liquid inside it.

Q.8. What is muscular force? Give one example.

The force generated by the action of muscles is called muscular force. It allows us to perform various physical activities.

For example, lifting a bucket of water involves muscular force.

Q.9. What is meant by gravitational force (or force of gravity)? Give one example.

Gravitational force is the force that pulls objects towards each other. It is responsible for the attraction between the Earth and objects on its surface. Key points about gravitational force:

• It acts on all objects, regardless of their size.
• Commonly observed when objects fall, like a coin or a pen.
• It causes water to flow downwards when a tap is opened.
• Every object in the universe exerts a gravitational force on every other object.

For example, when you drop a coin, it falls to the ground due to the force of gravity acting on it.

Q.10. Explain why the walls of a dam are thicker near the bottom than at the top. 

The walls of a dam are thicker at the bottom than at the top for several reasons:

• The pressure of the water increases with depth.
• Greater pressure at the bottom requires the dam to be stronger to withstand this force.
• A thicker structure at the base helps prevent failure or collapse.

Overall, the design ensures the dam remains stable and safe under the weight of the water.

Q.11. Explain why the frictional force is said to be a contact force. 

The frictional force is considered a contact force because:

• It acts on all moving objects.
• The direction of friction is always opposite to the direction of motion.
• Friction arises from the contact between surfaces.

Thus, it exemplifies a force that requires physical interaction.

Q.12. Explain why the tip of a sewing needle is sharp. 

The tip of a sewing needle is sharp for several important reasons:

• The sharp tip allows the needle to apply force on a very small area of the fabric.
• This concentration of force creates a large pressure, which is sufficient to pierce the cloth.
• A sharp needle makes stitching easier and more efficient.

Q.13. What do you understand by the state of Motion? 

The state of motion of an object is defined by its speed and direction. It can be summarised as follows:

• An object can be in one of two states: at rest or in motion.
• The state of rest is when the object has zero speed.
• Both states are considered part of the object's overall state of motion.

Q.14. Why does a plastic comb rub with dry hair attract tiny pieces of paper?

When a plastic comb is rubbed in dry hair, the comb gets electric charges by friction. And when this electrically charged comb is brought near tiny pieces of paper, it exerts an electrostatic force of attraction on them. Due to this electrostatic force, the tiny pieces of paper move towards the comb and stick to it.

Q.15. Explain why, when a person stands on a cushion, the depression is much more than when he lies down on it.

When a person stands on a cushion:

• Only their feet touch the cushion.
• This means their weight is concentrated on a small area.
• The result is a large amount of pressure, causing a significant depression in the cushion.

In contrast, when the same person lies down:

• Their entire body is in contact with the cushion.
• This spreads their weight over a larger area.
• Consequently, the pressure is much smaller, leading to only a slight depression.