## Topic outline

• ### Force

• Force

In our daily life, we often use our muscles to pull or push things: we pull up a glass of milk to get it to our mouth; we push an object to move in particular direction etc. We come to realize that either a “pull” or “push” is required to move an object. So, Force is a push or pull on an object.

We uses force to walk, to lift any object, to throw anything, to move any object from its place etc. In short, force is there in every activity we do. By applying force we usually bring anything in motion or in rest position but not always. Example: If we apply force on a wall it does not move.

Some application of force in everyday life

We pedal a cycle and cycle moves forward.

In bullock cart, a cart is being pulled by a bullock.

Two team pulling the rope in the game of tug of war.

We pull to open the door of our room.

Effects of force:

Force has many effects on the objects it is applied to. It can cause many changes to the object to which force is applied.

Force causes motion

Force can bring stationary object in motion provided there is no other force preventing the motion. When we apply force on any stationary object, it starts moving in the direction of force. A change in object’s position is called motion.

Example: When we push any toy car, it moves.

So, when force is applied, a stationary object comes in motion or force changes the position of stationary object.

Force changes the speed

Force changes the motion of body that is already in motion.

Example: When we push harder to moving toy car, its speed increases. Similarly we can apply force in opposite direction of the motion to slow down the speed of the toy car.

Therefore, we can say that force changes the speed of an object.

Force stops motion

When we apply more force in the opposite direction of the motion, an object stops moving.

Example: When we try to hold the ball thrown to us with force greater than the force with which it is coming, it stops.

Therefore, we can say that force can also stop a moving object.

Force change the direction

When a force is applied at an angle to a moving object, force changes the direction of the moving object.

Example:

In game of badminton, when player hit the shuttlecock back to the player on the opposite side, his force changes the direction of shuttlecock.

A moving car changes its direction when force is applied on its steering wheel so as to turn it.

In game of football, player changes the direction of moving football by hitting the ball by his foot at an angle.

Force changes the shape

When we force is applied on an object its shape and size changes.

Example:

When an inflated balloon is pressed, force applied changes its shape.

When we squeeze a plastic water bottle, force applied changes its shape and size.

Types of forces

There are many different kinds of force. Some of them are:

Muscular force

We brush our teeth, lift our bag, write with our hand, walk to the school, and get up from our desk. In all these activities we do use our muscles to apply force. The force applied by our muscles to carry out all our activities is called muscular force.

Example:

Potter applies his muscular force to give shape to his pots.

We apply muscular force to lift a box, ride a cycle, swim, walk etc.

Mechanical force

Force applied by a machine is called mechanical force.

Example:

Force applied by bulldozer to move the soil.

Force applied by digger to dig the earth.

Gravitational Force

When we throw a ball up in the sky, it comes down and when we jump, we come back on earth. Why this happens? This is the earth which pulls things towards it. That is why apple drop down on the ground from a tree instead of going into the sky. The pull of the earth is a kind of force. This force is called gravitational force. It is this pull of the earth which keeps us and other object on earth from drifting into space. This force was discovered by Sir. Isaac Newton.

Magnetic Force

A magnet is a material that attracts things made of iron, nickel and cobalt.

Force of magnet is called magnetic force.

Frictional Force

When we roll down a ball on grassy ground, it gradually slows down and finally stops. This happens because a force acts between the ball and the ground. Therefore, frictional force is the force exerted by a surface as an object moves across it or makes an effort to move across it.

Example: When we slide pencil across the surface of a desk, then the desk exerts a friction force in the opposite direction of its motion and pencil slow down and finally stops sliding.

Since friction slow down or prevent motion, it prevents us from slipping all the time, enable us to walk without falling, apply break in our vehicles, makes the movement of vehicle possible on road.

Frictional force is greater on rough surfaces such as grassy ground, on woolen clothes and lesser on smooth and slippery surface.