1. Newton's Universal Law of Gravitation
BHS Physical Science
K Warne

2. Mass & Weight G10 Revision Mass (kg):
This is a measure of the amount of matter (number of kilograms) that makes up a body.
1 kg
1 kg
1 kg Fg
Weight (N):
This is the force of gravity exerted on a body’s mass by the earth (planet).

3. Mass & Weight Mass (m): Measured in kilograms using a balance.
G10 Revision
Mass (m):
Measured in kilograms using a balance.
Force/Weight (Fg):
Measured in Newton's using a spring balance or force meter.
9.8N
1 kg

4. Falling Objects G10 Revision
Two different object with different masses will FALL at the same RATE.
1kg
9.8 N
5 kg
1kg
9.8 N
1kg
9.8 N
1kg
9.8 N
1kg
9.8 N
1kg
49 N
9.8 N
The force of gravity on 1kg of mass is 9.8 N.
Each unit of mass has the same force on it!
Each mass unit will have the SAME ACCELERATION.

5. Motion of Falling object
G10 Revision
Time (s)
Displacement (m)
Average Velocity
Instantaneous Velocity (m.s-1)
Acceleration (m.s-2) 5 20 45 4 80
125 6
180 1 2 3

6. Gravitational Field Strength & Acceleration
A gravitational field causes masses inside it to experience a force of attraction (weight) and therefore accelerate.
g = 9.8 N.kg-1 or m.s-2
Force
g = F/m
Gravitational field strength
= Gravitational Force per unit mass
Each kilogram of mass experiences 9.8 N of force!
Acceleration
g = F/m
Gravitational acceleration
= the rate at which a falling objects velocity increases
Falling objects fall 9.8 m.s-1 faster every second!
Calculate the weight of a 5 kg object on earth.
Calculate the velocity (on earth) of a falling object 3s after it is dropped from rest.
If and object weighs 300N what is its mass?
Use the equation for gravitational acceleration to SHOW that a 2kg object will accelerate at the same rate as a 10kg object.
If an object is thrown towards the earth with a velocity of 5m.s-1 calculate the velocity that it will hit the ground with if it falls for another 1.5 s. (Ignore friction)

7. Mass & Weight Examples Calculate the weight of a 75 kg person.
What would your mass be if you weighed 600 N?
What is the mass of an object which weighs 1 N?
Calculate the weight of the following:
a 500 g tub of margerine
0.2 g of sodium chloride
250 ml of water
A 300 mg gold nugget
What is the gravitational acceleration on a planet where a 50 kg object has a mass of 250 N?
What is the gravitational field strength if an object weighing 400N has a mass of 10 kg.
If a 4 kg object falls on a planet and gains 30 m.s-1 every 2s then calculate its weight.

9. Newton's Universal Law of Gravitationd m1 m2
The force of gravitational attraction that exists between two masses m1 & m2 is given by
d - is the distance of separation between their centres.

10. Relationship between Force, mass and distance.

11. Gravitational acceleration and Newton
Fg = G m1∙ m2 r2
Fg = G me∙ mo
re2
Mass of
Object = mo re
But since
Fg = mo∙ g (N 2)
mo∙ g = G me∙ mo
re2
Me = mass of the earth
re = distance between centres as object so small!
g = G me
re2

12. Gravitational Field Strength
A gravitational field causes masses inside it to experience a force of attraction.
Gravitational field strength = Gravitational Force per unit mass
g = F/m (N.kg-1)
g = 9.8 N.kg-1
g = 3.8 N.kg-1
g = 23.6 N.kg-1
Calculate the weight of a 5kg bag of sugar on each planet shown. N
5kg
......N
5kg
5kg
......N

13. Mass & Weight OBJECT MASS (kg) WEIGHT Shoe 0.5 Pen
Calculate the missing values in each of the following examples.
OBJECT
MASS (kg)
WEIGHT
Shoe
0.5
Pen

14. Newton’s gravitation examples
Calculate the mass of the earth using the accepted value for g (9.8 m.s-2) and the radius of the earth km.
What would your mass be on the moon?
The international space station which
orbits at an average height of 350 km.
Calculate your “weight” (w.r.t earth) on the
space station.
Why would you feel weightless?
Calculate your weight on the planet Jupiter which has a mass of × 1027 kilograms and a diameter of about km.
Calculate the mass of an earth size planet on which a 50 kg person would have a weight of 1000 N.