Questions and Answers
What is a force and how is it defined in science? Provide an example.
A force is a push or a pull on an object. In science, a push or pull on an object is called a force. For example, kicking a ball is applying force to it.
What can a force do to bodies on which it is applied?
When two forces act in the opposite directions on an object, the net force acting on it is always zero.
False
A force could be larger or smaller than the other. The strength of a force is usually expressed by its ___________.
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The force resulting due to the action of ____ is known as the muscular force.
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What is the force responsible for changing the state of motion of objects in the given examples?
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Gravity is a property specific to the Earth only.
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What is the force that causes objects to fall towards the Earth?
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Match the following forces with their descriptions:
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What is described as a change in its state of motion?
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What happens to the speed and direction of a moving ball when a force is applied in the direction of its motion?
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A force may change __________ of an object.
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Force can change the speed of an object but not its direction. True or False?
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Match the situation with the corresponding action of force:
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Why are shoulder bags provided with broad straps and not thin straps?
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Why do tools meant for cutting and piercing always have sharp edges?
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What happens to the bulge in the rubber sheet when more water is poured into the pipe?
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Air exerts pressure on the inner walls of an inflated balloon or tube.
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What is the name given to the pressure exerted by the air all around us?
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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. (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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To draw water from a well we have to ——— at the rope.
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A charged body ———— an uncharged body towards it.
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To move a loaded trolley we have to ———— it.
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The north pole of a magnet ———— the north pole of another magnet.
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To stretch the bow, the archer applies a force that causes a change in its ——.
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The force applied by the archer to stretch the bow is an example of ——— force.
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The type of force responsible for a change in the state of motion of the arrow is an example of a ———— force.
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While the arrow moves towards its target, the forces acting on it are due to ———— and that due to ———— of air.
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In the situation of squeezing a piece of lemon between the fingers to extract its juice, the agent exerting the force is ——— and the object on which it acts is ———.
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In the situation of taking out paste from a toothpaste tube, the agent exerting the force is ——— and the object on which it acts is ———.
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In the situation of a load suspended from a spring while its other end is on a hook fixed to a wall, the agent exerting the force is ——— and the object on which it acts is ———.
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In the situation of an athlete making a high jump to clear the bar at a certain height, the agent exerting the force is ——— and the object on which it acts is ———.
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How does the force due to hammering affect the piece of iron?
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What force might be responsible for the attraction between the balloon and the wall?
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What forces are acting on a plastic bucket containing water held above ground level in your hand?
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Why do the forces acting on the bucket do not bring a change in its state of motion?
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What are the two forces acting on the rocket immediately after leaving the launching pad?
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When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
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Study Notes
Force and Pressure
- A force is a push or pull that can make an object move, speed up, slow down, or change direction.
- Forces can be classified as pushes or pulls, and the motion of an object is due to the action of a force.
- Force is a result of an interaction between two objects, and at least two objects must interact for a force to come into play.
Characteristics of Force
- Forces can be applied in different directions, and the net force acting on an object is the sum of all forces acting on it.
- When two forces act in the same direction, they add up to a greater force; when they act in opposite directions, they cancel each other out.
- The strength of a force is expressed by its magnitude, and its effect on an object depends on the direction in which it acts.
Exploring Forces
- Forces can be applied by pushing, pulling, kicking, hitting, lifting, flicking, or throwing an object.
- More than one force can act on an object, and the net force determines the object's motion.
- When two forces act on an object in opposite directions, the net force is the difference between them.
A Force Can Change the State of Motion
- A force can increase or decrease the speed of an object, and change its direction of motion.
- When a force is applied to an object, it can change its state of motion, which is described by its speed and direction of motion.
- The state of rest is considered a state of zero speed.
A Force Can Change the Shape of an Object
- A force can be applied to an object to change its shape, such as when a force is applied to an inflated balloon by pressing it between the palms.
- The application of force on an object can change its shape, like when a ball of dough is rolled to make a chapati.
- Forces can also be used to deform or change the shape of an object, like when a rubber ball is pressed on a table.
Forces in Everyday Life
- Forces are used in various aspects of daily life, such as in sports, transportation, and construction.
- Understanding forces is essential to understand how objects move and respond to external influences.
- Forces are an integral part of our daily lives, and their effects are evident in the world around us.### Understanding Force and Pressure
Types of Forces
- Contact forces: Forces that require physical contact between objects, e.g., muscular force, frictional force
- Non-contact forces: Forces that do not require physical contact between objects, e.g., magnetic force, electrostatic force, gravitational force
Muscular Force
- Exerted by the muscles in our body
- Enables us to perform physical activities, e.g., lifting, pushing, pulling
- Also used by animals to carry out tasks
Frictional Force
- Arises due to contact between surfaces
- Opposes motion between two surfaces in contact
- Examples: slowing down of a rolling ball, stopping of a bicycle
Magnetic Force
- Exerted by magnets on other magnets or magnetic materials
- Can attract or repel depending on the poles of the magnets
- Does not require physical contact
Electrostatic Force
- Exerted by charged bodies on other charged or uncharged bodies
- Can attract or repel depending on the type of charge
- Does not require physical contact
Gravitational Force
- Attractive force between objects with mass
- Exerted by the Earth on objects on its surface
- Causes objects to fall towards the ground
Pressure
- Force acting on a unit area of a surface
- Pressure = force / area on which it acts
- Increases with decreasing area for the same force
- Examples: pointed end of a nail, sharp knife, broad straps on shoulder bags
Pressure Exerted by Liquids and Gases
- Liquids and gases exert pressure on the walls of their containers
- Pressure increases with the height of the liquid column
- Can cause bulging of flexible surfaces, e.g., rubber sheets### Pressure and Its Effects
- Pressure is force per unit area, and it can cause an object to change its shape or state of motion.
- Atmospheric pressure is the pressure exerted by the air surrounding us, and it is responsible for many natural phenomena.
- Liquids exert equal pressure at the same depth, as demonstrated by the experiment with the glass tube and plastic bottle.
- Gases also exert pressure on the walls of their containers, as seen in the example of a blown-up balloon.
Atmospheric Pressure
- Atmospheric pressure is the weight of air in a column of unit area, and it is approximately 1000 kg per 10 cm × 10 cm area.
- The pressure inside our bodies is equal to the atmospheric pressure, which is why we don't get crushed by it.
- Atmospheric pressure is responsible for many everyday phenomena, such as water coming out of a fountain or a leaking pipe.
Experiments with Pressure
- A rubber sucker can stick to a surface due to atmospheric pressure, and it's hard to pull it off because of the pressure.
- Otto von Guericke's experiment with the hemispheres demonstrated the force of air pressure, showing that it can be strong enough to resist the pull of eight horses.
- The experiment with the plastic bottle and holes shows that liquids exert equal pressure at the same depth.
Key Learnings
- Force can cause a change in the state of motion or shape of an object.
- A change in the speed of an object, 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 shape.
- A force can act on an object with or without being in contact with it.
- Liquids and gases exert pressure on the walls of their containers.
Keywords and Concepts
- Atmospheric pressure
- Contact force
- Electrostatic force
- Friction
- Gravity
- Magnetic force
- Muscular force
- Non-contact force
- Pressure
- Push
- Pull
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Description
This quiz is about understanding the concept of force and pressure in class 7, including how objects move and respond to external forces.
