1. CH 3: FORCES
3.2 GRAVITY

2. GRAVITY attractive force between two objects depends on:
1. mass of objects
2. distance between
objects
long-range force
because it never
goes to zero

3. Law of Universal Gravitation
enables the force of gravity to be calculated between any two objects if their masses and the distance between them are known

4. gravitational force between two objects decreases rapidly as the distance between them increases
hvo.wr.usgs.gov

5. free fall ignore all forces acting on an object except gravity
close to the Earth’s surface, acceleration of an object is 9.8 m/s2 (acceleration due to gravity)

6. weight
gravitational force exerted on an object

7. MASS is the amount of matter an object contains
WEIGHT is the force of gravity on that mass
therefore, note: weight is measured in Newton’s

8. Weight on Earth versus other planets site

9. projectile motion
anything thrown or shot through the air is in projectile motion
it is ALWAYS in a curved path due to gravity
path shows both horizontal and vertical motion

10. click on image to play video

11. centripetal force net force exerted toward the center of a curved path
the acceleration in a curved path is also toward the center (centripetal acceleration)
Car travels in a curved path because of
centripetal force. This force is a frictional
force between the tires and the road. If
the friction decreases, the centripetal
force may not be strong enough to keep
the car in a curved path – it would
travel in a straight line.

12. Gravitational Force and Weight Problems
Q1: How much force is used to lift a 25 kg mass?
Mass and Acceleration due to gravity
What is known?
What are we solving for?
Force
Equation:
F = M x A
F = 25 kg x 9.8 m/s2
F= 245 N
Solve:

13. Q2: A person on an elevator moves downward with an acceleration of 1
Q2: A person on an elevator moves downward with an acceleration of 1.8 m/s2. If the person weighs 686 N, what is the mass of the person?
What is known?
Acceleration and Weight
Solve for:
Mass
Equation:
Weight = Mass x Acceleration
W= mg therefore m= w/g
M= 686 N/ 1.8 m/s2
M= kg
Solve: