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?
Forces acting in the same direction on an object add up to each other.
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What is the force resulting due to the action of muscles known as?
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What is the force responsible for changing the state of motion of objects in various examples mentioned in the text?
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Is the force exerted by a magnet on another magnet a non-contact force?
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The force exerted by a charged body on another charged or uncharged body is known as ____________ force.
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Match the following forces with their corresponding examples:
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What is the formula for pressure?
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Why do porters place a round piece of cloth on their heads when carrying heavy loads?
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Why do shoulder bags have broad straps?
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Liquids exert pressure on the walls of the container.
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Gases also exert pressure on the walls of their containers.
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What is atmospheric pressure?
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Why does the rubber sucker stick to the surface?
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Why can't you pull the sucker off the surface?
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What is described as a change in the state of motion of an object?
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What may happen when you apply a force on an object?
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A force may bring a change in the __________ of an object.
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An object can move, change speed, change direction, or change shape without the action of a force.
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Give two examples each of situations in which you push or pull to change the state of motion of objects.
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Give two examples of situations in which applied force causes a change in the shape of an object.
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(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.
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Give two examples each of situations in which you push or pull to change the state of motion of objects.
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Give two examples of situations in which applied force causes a change in the shape of an object.
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(a) To draw water from a well we have to ______ at the rope.
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(b) A charged body ______ an uncharged body towards it.
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(c) To move a loaded trolley we have to ______ it.
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(d) The north pole of a magnet ______ the north pole of another magnet.
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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.
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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
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Forces are pushes or pulls on an object.
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Forces can change the state of motion of an object.
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Forces can change the shape of an object.
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Forces occur due to interaction between two objects.
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The strength and direction of a force affect its effect on an object.### Force and Motion
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A force is required to change the state of motion of an object.
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A force can make an object move from rest, change its speed, direction, or shape.
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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.
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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
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Pressure is the force acting on a unit area of a surface.
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Pressure is dependent on the area on which the force acts, and it is inversely proportional to the area.
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A smaller area of application of force results in a greater pressure on the surface.
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Pressure is used in everyday life, such as in cutting vegetables with a sharp knife, or carrying heavy loads with broad straps.
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Liquids and gases also exert pressure, and it depends on the area on which the force acts.
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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
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Fix a cylindrical glass tube near its bottom as shown in Fig. 11.15.
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Heat one end of the glass tube and quickly insert it near the bottom of a plastic bottle or cylindrical container.
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Drill four holes all around near the bottom of the bottle, making sure they are at the same height from the bottom.
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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.
Force and Pressure
- Force can be a push or a pull.
- A force arises due to the interaction between two objects.
- Force has magnitude as well as direction.
- A change in the speed of an object or the direction of its motion or both implies a change in its state of motion.
- Force acting on an object may cause a change in its state of motion or a change in its shape.
- Force per unit area is called pressure.
- Liquids and gases exert pressure on the walls of their containers.
- The pressure exerted by air around us is known as atmospheric pressure.
Keywords
- Atmospheric pressure
- Contact force
- Electrostatic force
- Friction
- Gravitational force
- Magnetic force
- Muscular force
- Non-contact force
- Pressure
- Push
- Pull
Exercises
- Give two examples each of situations in which you push or pull to change the state of motion of objects.
- Give two examples of situations in which applied force causes a change in the shape of an object.
- Fill in the blanks in the following statements:
- To draw water from a well, we have to ——— at the rope.
- A charged body ———— an uncharged body towards it.
- To move a loaded trolley, we have to ———— it.
- The north pole of a magnet ———— the north pole of another magnet.
- An archer stretches her bow while taking aim at the target, applying muscular force, contact force, and gravity.
- Identify the agent exerting the force and the object on which it acts in various situations.
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Description
Test your understanding of force and pressure in Class 7. Learn how objects move and how to decide whether an object is moving or not.