1. Gravity and The Law of Universal Gravitation
3.1.2

2. What is Gravity?
Gravity is an attractive force between any two objects that depends on the masses of the objects and the distance between them.
Gravity increases:
as the mass increases
as the distance decreases

3. Who experiences more gravity - the astronaut or the politician?
Which exerts more gravity - the Earth or the moon?
more mass
less distance

5. The Law of Universal Gravitation
The law of universal gravitation lets us find the force of gravity between any two objects if their masses and the distance between them are known.

6. F = G m1 m2 d2 F = gravitational force
G = universal gravitational constant
variable d = distance between the two masses,m1 and m2
Enables the force of gravity to be calculated between 2 objects

7. The Gravitational Field
Gravity is called a long-range force.
Gravity never disappears.
All objects are surrounded by a gravitational field.
The strength of the gravitational field (g) is 9.8 N/kg near Earth’s surface and gets smaller as you move away from Earth.
g = 9.8 N/kg
N – Newton
1 N = 1 kg . m/s2

8. Is there a difference between weight and mass?
the force of gravity on an object
Mass
measure of the amount of matter in an object
Weight and mass are related.
The greater an object’s mass, the stronger the gravitational force between the object and Earth.

9. Would you weigh more on Earth or Jupiter?
Jupiter because...
greater mass
greater gravity
greater weight

10. Fg = mg Weight the force of gravity on an object WEIGHT MASS
Fg - weight (N)
m - mass (kg)
g - acceleration due to gravity (m/s2)
WEIGHT
depends on gravity
(N)
MASS
always the same
(kg)

11. m = 5000 kg g = 9.8 N/kg Fg = elephants weight Fg = mg
An elephant has a mass of 5000 kg. What is the elephant’s weight?
What is given?
What is unknown?
Which formula?
Set up problem and show work.
Does your final answer have the correct unit?
m = 5000 kg
g = 9.8 N/kg
Fg = elephants weight
Fg = mg
Fg = 5000 kg N/kg
Fg = 49,000 N

12. What is the gravitational force exerted on an object called?
Assessment
What is the gravitational force exerted on an object called? 1.
centripetal force A
friction B
momentum C
weight D
CORRECT

13. The spacecraft is in free fall.
Assessment 2.
Which explains why astronauts seem weightless in orbit?
Earth’s gravity is much less in orbit. A
The spacecraft is in free fall. B
CORRECT
The gravity of Earth and the Sun cancel. C
The centripetal force on the shuttle balances Earth’s gravity. D

14. Assessment 3.
Which term best describes the forces on an object with a net force of zero?
balanced forces A
CORRECT
unbalanced forces B
inertia C
acceleration D

15. Which body exerts the strongest gravitational force on you?
Assessment 4.
Which body exerts the strongest gravitational force on you?
the Moon A
Earth B
CORRECT
the Sun C
this book D

16. Assessment 5.
The graph shows the speed of a car moving in a straight line. Over which segments are the forces on the car balanced?
A and C A
B and D B
CORRECT
C and E C
A, C, and E D

17. Which of the following is not a force?
Assessment 6.
Which of the following is not a force?
weight A
friction B
momentum C
CORRECT
air resistance D