Force and Pressure Class 7
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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?

  • Make them move faster
  • Make them move slower
  • Change their direction of motion
  • All of the above (correct)

    • 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 ___________.

    <p>magnitude</p> Signup and view all the answers

    The force resulting due to the action of ____ is known as the muscular force.

    <p>muscles</p> Signup and view all the answers

    What is the force responsible for changing the state of motion of objects in the given examples?

    <p>force of friction</p> Signup and view all the answers

    Gravity is a property specific to the Earth only.

    <p>False</p> Signup and view all the answers

    What is the force that causes objects to fall towards the Earth?

    <p>Force of gravity</p> Signup and view all the answers

    Match the following forces with their descriptions:

    <p>Electrostatic Force = Force exerted by charged bodies on other charged or uncharged bodies Gravitational Force = Force that acts on all objects, pulling them towards the Earth Magnetic Force = Force exerted by magnets on other objects without contact Force of Friction = Force that opposes the motion of objects on surfaces</p> Signup and view all the answers

    What is described as a change in its state of motion?

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

    What happens to the speed and direction of a moving ball when a force is applied in the direction of its motion?

    <p>Speed increases, direction remains the same</p> Signup and view all the answers

    A force may change __________ of an object.

    <p>the shape</p> Signup and view all the answers

    Force can change the speed of an object but not its direction. True or False?

    <p>False</p> Signup and view all the answers

    Match the situation with the corresponding action of force:

    <p>A lump of dough on a plate = Change in shape Spring fixed to the seat of a bicycle = Change in state of motion A rubber band suspended from a wall = Change in state of motion A plastic or metal scale between two bricks = Change in shape</p> Signup and view all the answers

    Why are shoulder bags provided with broad straps and not thin straps?

    <p>To reduce pressure on the shoulders by distributing the force over a larger area.</p> Signup and view all the answers

    Why do tools meant for cutting and piercing always have sharp edges?

    <p>To increase pressure on the surface being cut or pierced.</p> Signup and view all the answers

    What happens to the bulge in the rubber sheet when more water is poured into the pipe?

    <p>The bulge increases.</p> Signup and view all the answers

    Air exerts pressure on the inner walls of an inflated balloon or tube.

    <p>True</p> Signup and view all the answers

    What is the name given to the pressure exerted by the air all around us?

    <p>Atmospheric pressure</p> 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.

    <p>Examples may include pushing a swing to make it move forward or pulling a drawer to open it.</p> Signup and view all the answers

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

    <p>Examples may include stretching a rubber band or bending a piece of wire.</p> 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.

    <p>Answers may vary but could include pushing a swing to start it moving or pulling a door to open it.</p> Signup and view all the answers

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

    <p>Answers may vary but could include compressing a spring or bending a spoon.</p> 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.

    <p>Examples: pushing a box to move it, pulling a rope to lift a load, etc.</p> Signup and view all the answers

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

    <p>Examples: hammering a nail to bend it, squeezing a piece of clay to change its shape, etc.</p> Signup and view all the answers

    To draw water from a well we have to ——— at the rope.

    <p>pull</p> Signup and view all the answers

    A charged body ———— an uncharged body towards it.

    <p>attracts</p> Signup and view all the answers

    To move a loaded trolley we have to ———— it.

    <p>push</p> Signup and view all the answers

    The north pole of a magnet ———— the north pole of another magnet.

    <p>repels</p> Signup and view all the answers

    To stretch the bow, the archer applies a force that causes a change in its ——.

    <p>shape</p> Signup and view all the answers

    The force applied by the archer to stretch the bow is an example of ——— force.

    <p>muscular</p> Signup and view all the answers

    The type of force responsible for a change in the state of motion of the arrow is an example of a ———— force.

    <p>contact</p> Signup and view all the answers

    While the arrow moves towards its target, the forces acting on it are due to ———— and that due to ———— of air.

    <p>gravity and friction</p> Signup and view all the answers

    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 ———.

    <p>fingers and lemon</p> Signup and view all the answers

    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 ———.

    <p>hand and tube</p> Signup and view all the answers

    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 ———.

    <p>spring and load</p> Signup and view all the answers

    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 ———.

    <p>athlete and ground</p> Signup and view all the answers

    How does the force due to hammering affect the piece of iron?

    <p>It changes its shape.</p> Signup and view all the answers

    What force might be responsible for the attraction between the balloon and the wall?

    <p>electrostatic</p> Signup and view all the answers

    What forces are acting on a plastic bucket containing water held above ground level in your hand?

    <p>gravity and atmospheric pressure</p> Signup and view all the answers

    Why do the forces acting on the bucket do not bring a change in its state of motion?

    <p>They are balanced.</p> Signup and view all the answers

    What are the two forces acting on the rocket immediately after leaving the launching pad?

    <p>thrust and gravity</p> Signup and view all the answers

    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

    <p>atmospheric pressure</p> Signup and view all the answers

    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.

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