1) a. Force affects the body and results in different changes. The grid given below has the words related to the effects of force. Find those words. b. Write about the effects of force you found in the grid with two examples each.
Answers
Answer:
scale placed
between two bricks By putting a weight
at the centre of the
scale
Tab No Yes
Contact Forces
Muscular Force
Can you push or lift a book lying on a table without touching it? Can you lift a bucket of water without holding it?Generally, to apply a force on an object, your body has to be in contact with the object. The contact may also be with the help of a stick or a piece of rope. When we push an object like a school bag or lift a bucket of water, where does the force come from? This force is causedby the action of muscles in our body. The force resulting due to the action of muscles is known as the muscular force.
Animals also make use of muscular force to carry out their physical activities and other tasks.Animals like bullocks, horses, donkeys and camels are used to perform various tasks for us. In performing these tasks they use muscular force.
Since muscular force can be applied only when it is in contact with an object, it is also called a contact force. It is the muscular force that enables us to perform all activities involving movement or bending of our body.
Friction
A ball rolling along the ground gradually slows down and finally comes to rest. When we stop pedalling a bicycle, it gradually slows down and finally comes to a stop. A car or a scooter also comes to rest once its engine is switched off. Similarly, a boat comes to rest if we stop rowing it. In all these situations no force appears to be acting on the objects, yet their speed gradually decreases and they come to rest after some time. What causes a change in their state of motion? Could some force be acting on them! Can you guess the direction in which the force must be acting in each case?
The force responsible for changing the state of motion of objects in all these examples is the force of friction. It is the force of friction between the surface of the ball and the ground that brings the moving ball to rest. Similarly, friction between water and the boat brings it to a stop once you stop rowing.
The force of friction always acts on all the moving objects and its direction is always opposite to the direction of motion. Since the force of friction arises due to contact between surfaces, it is also an example of a contact force. You may be wondering whether it is essential for the agent applying a force on an object to be always in contact with it. Let us find out
Non-contact Forces
Magnetic Force
A a
Gravitational Force
You know that a coin or a pen falls to the ground when it slips off your hand. The leaves or fruits also fall to the ground when they get detached from the plant. When the coin is held in your hand it is at rest. As soon as it is released, it begins to move downwards. It is clear that the state of motion of the coin undergoes a change.
Objects or things fall towards the earth because it pulls them. This force is called the force of gravity, or just gravity. This is an attractive force. The force of gravity acts on all objects. The force of gravity acts on all of us all the time without our being aware of it. Water begins to flow towards the ground as soon as we open a tap. Water in rivers flows downward due to the force of gravity.
Gravity is not a property of the earth alone. In fact, every object in the universe, whether small or large, exerts a force on every other object. This force is known as the gravitational force.
Summary
Force could 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.
A force can act on an object with or without being in contact with it.