1. Mass and Weight This is the amount of matter. (Kg)
This is the force of gravity pulling on the mass. (N)
* less on the moon , zero in deep space.
There is a very, small force
of attraction between
an apple and an orange.
* too small to measure!

2. Weight vs. Mass
Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. W g M
Weight = Mass x Gravitational Field Strength
(in N) (in kg) (in N/kg)
What is the weight on Earth of a book with mass 2kg?
What is the weight on Earth of an apple with mass 100g?
Dave weighs 700N. What is his mass?
On the moon the gravitational field strength is 1.6N/kg. What will Dave weigh if he stands on the moon?

3. Forces on falling objects
1. Object falling freely
Forces Acting
Motion

4. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration

5. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration

6. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration
Object in air

7. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration
Object in air

8. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration
( …….. m/s/s)
Object in air
acceln = gradient

9. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration
( …….. m/s/s)
Object in air
acceln = gradient

10. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration
(10 m/s/s)
Object in air

11. Forces on falling objects
1. Object falling freely
Forces Acting
Motion
the force of gravity
(weight)
Uniform acceleration
(10 m/s/s)
If a 1kg mass is released above the ground
* the force of gravity on it is 10N
* its acceleration is force = 10N =10m/s/s
mass Kg

12. 2. Object falling through a fluid
Forces Acting
Motion
force of gravity (weight)
* initial acceleration (10 m/s/s) *
Object in air

13. 2. Object falling through a fluid
Forces Acting
Motion
force of gravity (weight)
* initial acceleration (10 m/s/s)
* decreasing acceleration to zero
* terminal velocity
Drag force (air resistance)
Buoyancy (upthrust)
Object in air

14. 2. Object falling through a fluid
Forces Acting
Motion
force of gravity (weight)
* initial acceleration (10 m/s/s)
* decreasing acceleration to zero
* terminal velocity
Drag force (air resistance)
Buoyancy (upthrust)
Object in air

15. Terminal Velocity Consider a skydiver:
At the start of his jump the air resistance is _______ so he _______ downwards.

16. Terminal Velocity Consider a skydiver:
At the start of his jump the air resistance is _______ so he _______ downwards.
2) As his speed increases his air resistance will _______

17. Terminal Velocity Consider a skydiver:
At the start of his jump the air resistance is _______ so he _______ downwards.
2) As his speed increases his air resistance will _______
3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITY

18. Terminal Velocity Consider a skydiver:
4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____.
5) Because he is slowing down his air resistance will _______ again until it balances his _________. The skydiver has now reached a new, lower ________ _______.

19. Velocity-time graph for terminal velocity…
Parachute opens – diver slows down
Velocity
Speed increases…
Terminal velocity reached…
On the Moon
Diver hits the ground
New, lower terminal velocity reached
Time

20. less than
equal to
equal to