4. WHAT IS FRICTION?
A force where two forces acting in opposing directions
on a body, are not equal in magnitude and in size, is
known as an unbalanced force.
Friction is the force that resists motion when the surface
of one object comes in contact with the surface of
another.
Friction plays in opposite direction of force.
TYPES OF FORCES
5. WHAT CAUSES FRICTION?
When we see any object, we can see the smooth surface
but when the same object is viewed under a it can be
microscope, seen that even the smooth appearing object
has rough edges.
Friction occurs because of rough surface.
TYPES OF FORCES
6. WHAT CAUSES FRICTION?
Friction is dependent on the smoothness or roughness of
the two surfaces that are in contact with each other.
When the surface is smooth, the friction between the
two reduces. While the surface is rough, friction
increases.
TYPES OF FORCES
7. REDUCING FRICTION
Friction can be minimized by using lubricants like oil and
grease and by using ball bearing between machine parts.
A substance that is introduced between two surfaces in
contact, to reduce friction, is called a lubricant.
Polishing and waxing can make object smoother by
removing bumps and filling some hollows which can
reduce friction.
TYPES OF FORCES
8. USEFUL FRICTION
Friction can be useful.
Example:
Friction between our shoes and the floor stop us from
slipping.
Friction between tyres and the road stop cars from
skidding.
TYPES OF FORCES
9. FRICTION FORCE
Here, two situations are given mention in which situation friction force is more and why?
TYPES OF FORCES
10. WHAT IS GRAVITY?
What do you known about gravity ?
Gravity pulls things to
the center of the Earth.
Gravity pulls on things
on earth but not in
space, astronauts float.
Gravity pulls things and
makes them fall down.
Gravity only pulls on
things that are falling.
TYPES OF FORCES
11. Gravitational force is a non-contact force that attract
objects to each other. Earth's gravitational force attracts
us downwards (towards the centre of the Earth).
TYPES OF FORCES
WHAT IS GRAVITY?
12. As we go away from earth the gravity becomes weaker.
This shows that gravity depends on distance.
EFFECT OF GRAVITY
TYPES OF FORCES
13. MASS OR WEIGHT?
We often use mass and weight interchangeably in
everyday speech. However, they are different things.
W = mg
Gravitational field strength
Mass
Weight
TYPES OF FORCES
14. The amount of matter in an object is called as mass.
It is usually measured in kilograms (kg), but It can be
measured in grams (g) or tonnes (t).
MASS
Mass Kg
TYPES OF FORCES
15. Weight is a pulling force which depends upon
gravitational force and mass of the object.
Weight = mass x gravity
W = m x g
Like all other forces, weight is also measured in
Newtons (N).
10m/s2
On Earth, gravitational force is about
WEIGHT
TYPES OF FORCES
16. Beam balance to measure mass
Spring balance to measure weight
MEASURNG WEIGHT AND MASS
TYPES OF FORCES
17. The upward force applied by the fluid on the object or
the body when an object is put in or submerged in the
fluid which causes a body to float.
BUOYANCY
TYPES OF FORCES
18. Hot Air Balloon
The atmosphere is filled with air that exerts buoyant
force on any object. A hot air balloon rises and floats
due to the buoyant force.
It descends when the balloon’s weight is higher than the
buoyant force. It becomes stationary when the weight
equals the buoyant force.
APPLICATIONS OF BUOYANCY
TYPES OF FORCES
19. Submarine
A submarine has a large ballast tank, which is used to
control its position and depth from the surface of the sea.
A submarine submerges by letting water into the ballast
tank so that its weight becomes greater than the buoyant
force.
APPLICATIONS OF BUOYANCY
TYPES OF FORCES
20. Ship
A ship floats on the surface of the sea because the
volume of water displaced by the ship is enough to have
a weight equal to the weight of the ship.
A ship is constructed in a way so that the shape is
hollow, to make the overall density of the ship lesser
than the sea water.
Therefore, the buoyant force acting on the ship is large
enough to support its weight.
APPLICATIONS OF BUOYANCY
TYPES OF FORCES
21. Surface tension is the tension of the surface film of a
liquid caused by the attraction of the particles in the
surface layer by the bulk of the liquid, which tends to
minimize surface area. All water particles are attached
together by cohesion force.
SURFACE TENSION
TYPES OF FORCES
