2. Force
A push or pull acting on an object is called force.
Examples- A man pushing a cart, a child pulling a toy
wagon, and a girl opening a door.
3. Effects of force
Force can make a stationary object move or make a
moving object move faster.
Force can make a moving object slow down or stop.
Force can change the direction of a moving object.
Force can change the shape of an object.
4. Types of Forces
Gravitational force or Gravity- It is the force that
attract objects to the centre of the earth.
If we throw a ball up, it comes down after some time
because of gravity.
We and all other objects are stable on the ground
because of Earth’s gravity.
5. Magnetic force or magnetism- It is the force with which
a magnet attracts metals such as iron and nickel, and
other magnets.
Magnets may also repel each other with the help of a
magnetic force.
6. Electrostatic force- The force that a charged body
exerts on another charged body is called electrostatic
force.
If we rub a comb on our dry hairs, the comb gets
charged and is able to attract tiny bits of paper when
brought near it.
7. Mechanical force- A mechanical force comes into play
when a pull or push comes in physical contact with an
object.
When we open a door, our hand pushes
the door, opening it.
Mechanical force can bend, break,
or compress things.
8. Buoyant force- When an object is
dropped in water, the water exerts a net
upward force that pushes the object up.
This upward force is called buoyant force.
The buoyant force is equal to the weight of
the water displaced by the object. This is
known as Archimedes’ principle.
9. Frictional force or friction- It is the force that tries
to stop the movement of objects across a surface.
Friction always acts in the direction opposite to the
direction of movement of an object.
It can slow down the movement of an object or stop it
from moving altogether.
10.
11. Advantages of Friction
Friction between our feet and the ground makes it
possible for us to walk.
We find it hard to walk on ice or on a smooth, polished
floor as movement across these surfaces produces less
friction. That is why we often slip on an icy ground or a
wet floor.
The friction between the tyres of vehicles and the road
makes them roll forward.
Friction between the chalk and the blackboard makes it
possible for teacher to write on the blackboard.
12.
13. Disadvantages of Friction
Friction makes it hard to slide heavy objects
across the floor.
Friction generates heat.
Friction causes damage to tyres of vehicles,
the soles of shoes and sleepers, and
machine parts making these objects wear
away with time. This is the reason why
machine parts need to be oiled regularly. Oil
is slippery and reduces the friction between
different parts of a machine.
