Download Forces

Effect of Exercise on Breathing Rate
• During exercise the breathing rate increases.
• This is because the cells of the body need to
make energy, so they require more oxygen for
respiration.
• After a rest, the breathing rate returns to normal.
• This is because the cells of the body don’t
require as much oxygen for respiration.
Force and Work
What is a Force?
• A force is something that
causes an object to accelerate.
• The unit of force is the Newton
(N).
• Force is measured using a
spring balance.
(also called a Newton-meter)
Examples of Forces and Their Effects
Force
Weight
Push
Effect
Moves objects towards the centre of the earth
Moves/increases speed or an object or
changes direction
Friction
Slows down objects moving over each other
Stretching
Changes the shape of an object
Compression Changes the shape of an object
Weight
• The weight of an object is the
force of gravity on it.
 Recall: Mass is the amount of
matter in an object.
• If you went to the moon, you
would have the exact same mass,
but you would have a different
weight, due to less gravity.
How to Calculate Weight on Earth
Weight
(in Newtons)
= Mass x 10
(in kg)
Example 1:
The mass of an object is 15kg. Calculate it weight.
Weight
Weight
Weight
= Mass (in kg) x 10
= 15
x 10
= 150 N
Example 2:
The mass of a packet of biscuits is 200g. Calculate its
weight.
First: Convert grams into kilograms (1kg = 1,000g)
200g = 200g ÷ 1000 = 0.2 kg
1000
Then: Convert mass into weight.
Weight = Mass (in kg) x 10
Weight = 0.2 x 10
Weight = 2 N
Friction
Friction is a force which opposes motion
between two objects in contact.
Advantages of Friction
Allows things to slow down or stop.
E.g. when a car’s brakes are applied, the friction between the
tyres and the ground allow it to stop
Allows us to walk, prevents us from slipping
on ground
Allows us to pick objects up, they don’t slip
out of our hands
Disadvantages of Friction
Slows things down.
E.g. friction between ships and water prevents them from
travelling too fast
Can wear away surfaces in contact with each other.
E.g. car tyres can be worn down
Lubrication
A lubricant is a substance that prevents friction.
Lubricants help substances to slide over each
other.
Examples of Lubricants:
• Ice on roads
• Soap on your hands
• Oil used in engines