Force and Pressure Class 7

Questions and Answers

What is a force in science?

A push or a pull on an object

What happens to the motion of an object when a force is applied?

It results in some kind of change in the motion of the object

What do interactions between objects result in?

Force (correct)

Acceleration

Friction

Motion

Forces acting in the same direction on an object add up to each other.

True Signup and view all the answers

What is the force resulting due to the action of muscles known as?

muscular force Signup and view all the answers

What is the force responsible for changing the state of motion of objects in various examples mentioned in the text?

Force of friction Signup and view all the answers

Is the force exerted by a magnet on another magnet a non-contact force?

True Signup and view all the answers

The force exerted by a charged body on another charged or uncharged body is known as ____________ force.

electrostatic Signup and view all the answers

Match the following forces with their corresponding examples:

Gravitational force = Force that pulls objects towards the earth Magnetic force = Force exerted by a magnet on a piece of iron Electrostatic force = Force between charged bodies Signup and view all the answers

What is the formula for pressure?

pressure = force / area on which it acts Signup and view all the answers

Why do porters place a round piece of cloth on their heads when carrying heavy loads?

To reduce the pressure on their head Signup and view all the answers

Why do shoulder bags have broad straps?

To reduce the pressure on the shoulder Signup and view all the answers

Liquids exert pressure on the walls of the container.

True Signup and view all the answers

Gases also exert pressure on the walls of their containers.

True Signup and view all the answers

What is atmospheric pressure?

The pressure exerted by the air in the atmosphere Signup and view all the answers

Why does the rubber sucker stick to the surface?

Because of the pressure of the atmosphere Signup and view all the answers

Why can't you pull the sucker off the surface?

Because the applied force is not enough to overcome the atmospheric pressure Signup and view all the answers

What is described as a change in the state of motion of an object?

A change in either the speed of an object, or its direction of motion, or both. Signup and view all the answers

What may happen when you apply a force on an object?

All of the above. Signup and view all the answers

A force may bring a change in the __________ of an object.

shape Signup and view all the answers

An object can move, change speed, change direction, or change shape without the action of a force.

False Signup and view all the answers

Give two examples each of situations in which you push or pull to change the state of motion of objects.

Pushing a swing to make it move, Pulling a box to slide it across the floor Signup and view all the answers

Give two examples of situations in which applied force causes a change in the shape of an object.

Squeezing playdough to form a shape, Stretching a rubber band Signup and view all the answers

(a) To draw water from a well we have to at the rope. (b) A charged body an uncharged body towards it. (c) To move a loaded trolley we have to it. (d) The north pole of a magnet the north pole of another magnet.

Signup and view all the answers

Give two examples each of situations in which you push or pull to change the state of motion of objects.

Pushing a swing to make it move forward; Pulling a wagon to move it. Signup and view all the answers

Give two examples of situations in which applied force causes a change in the shape of an object.

Stretching a rubber band until it deforms; Squeezing clay to make a shape. Signup and view all the answers

(a) To draw water from a well we have to ______ at the rope.

pull Signup and view all the answers

(b) A charged body ______ an uncharged body towards it.

attracts Signup and view all the answers

(c) To move a loaded trolley we have to ______ it.

push Signup and view all the answers

(d) The north pole of a magnet ______ the north pole of another magnet.

repels Signup and view all the answers

An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Fill in the gaps.

(a) To stretch the bow, the archer applies a force that causes a change in its shape. (b) The force applied by the archer to stretch the bow is an example of muscular force. (c) The type of force responsible for a change in the state of motion of the arrow is an example of a contact force. (d) While the arrow moves towards its target, the forces acting on it are due to gravity and that due to friction of air. Signup and view all the answers

Study Notes

What is a Force?

A force is a push or a pull on an object.
It can make an object move faster, slower, or change its direction.
Examples of forces include kicking, throwing, pushing, and pulling.

Forces in Everyday Life

We experience forces in our daily lives, such as when we open a door, kick a ball, or lift a heavy object.
Forces can be grouped into pushes or pulls.
To move an object, it has to be pushed or pulled.

Forces Due to Interaction

A force comes into play when two objects interact with each other.
At least two objects must interact for a force to occur.
The interaction of one object with another object results in a force between the two objects.

Exploring Forces

Forces can be applied in different directions, such as pushing or pulling an object.
The strength of a force is usually expressed by its magnitude.
The direction of the force applied on an object also affects its motion.

Forces and Motion

A force can change the state of motion of an object.
The state of motion of an object is described by its speed and direction of motion.
A force can increase or decrease the speed of an object, or change its direction of motion.

Forces and Shape

A force can change the shape of an object.
Examples of forces changing the shape of an object include pressing a balloon, rolling a ball of dough, or pressing a rubber ball.

Key Points

Forces are pushes or pulls on an object.
Forces can change the state of motion of an object.
Forces can change the shape of an object.
Forces occur due to interaction between two objects.
The strength and direction of a force affect its effect on an object.### Force and Motion
A force is required to change the state of motion of an object.
A force can make an object move from rest, change its speed, direction, or shape.
The application of force does not always result in a change in motion, as seen with a heavy box that may not move even when maximum force is applied.
A force can also cause an object to change its shape, as seen with a lump of dough.

Contact Forces

Muscular force is a type of contact force that is used to perform various physical activities, such as lifting a bucket of water or pushing a school bag.
Muscular force is applied when an object comes into contact with the body, and it is essential for performing daily tasks.
Animals also use muscular force to carry out their physical activities, such as bullocks, horses, and camels.
Friction is another type of contact force that acts between surfaces in contact, such as between a ball and the ground, or between water and a boat.

Non-contact Forces

Magnetic force is a type of non-contact force that can act on an object without being in contact with it.
Like poles of two magnets repel each other, while unlike poles attract each other.
Electrostatic force is another type of non-contact force that acts between charged bodies, and it can also act on uncharged bodies.
Gravity is a type of non-contact force that pulls objects towards each other, such as the force of the Earth on an object.

Pressure

Pressure is the force acting on a unit area of a surface.
Pressure is dependent on the area on which the force acts, and it is inversely proportional to the area.
A smaller area of application of force results in a greater pressure on the surface.
Pressure is used in everyday life, such as in cutting vegetables with a sharp knife, or carrying heavy loads with broad straps.
Liquids and gases also exert pressure, and it depends on the area on which the force acts.
The pressure exerted by a liquid or gas increases with the height of the column or the volume of the substance.### Activity 11.10: Fixing a Cylindrical Glass Tube
Fix a cylindrical glass tube near its bottom as shown in Fig. 11.15.
Heat one end of the glass tube and quickly insert it near the bottom of a plastic bottle or cylindrical container.
Drill four holes all around near the bottom of the bottle, making sure they are at the same height from the bottom.
Fill the bottle with water and observe what happens.

Atmospheric Pressure

The air around us, known as the atmosphere, extends up to many kilometers above the surface of the earth.
The pressure exerted by this air is known as atmospheric pressure, which is the force per unit area.
Atmospheric pressure can be demonstrated by imagining a unit area and a very long cylinder standing on it, filled with air.
The weight of the air in this cylinder is the atmospheric pressure.

Activity 11.11: Rubber Sucker

Take a good quality rubber sucker and press it hard on a smooth plane surface.
The sucker sticks to the surface because the pressure of the atmosphere acts on it.
To pull the sucker off the surface, the applied force should be large enough to overcome the atmospheric pressure.