1. DAILY QUESTION
January 14, 2009
What is the universal gravitation equation?

2. Agenda 1/14/09 Daily Question Check-in: 11-1 Wksht
Ch 11 Section 2 Notes
Assignments:
1. No assignment

3. Law of Universal Gravitation
All objects in the universe attract each other through gravitational force
F = G m1m d2
G represents a universal constant

4. ↑F = G ↑m1m d2
Gravitational force increases when: mass increases
↓F = G m1m ↑d2
Gravitational force decreases when: distance increases

5. No matter how large or small an object is, every object exerts a gravitational force

6. Gravitational Force increases as mass increases
Figure 6 on page 353.
When objects have larger masses, the gravitational force is larger
We live on Earth that has a large mass, therefore a large gravitational force.
That is why apples fall to the ground
An elephant has a large mass and therefore a greater gravitational force
That is why they are harder to pick up than a kitty cat

7. Gravitational force decreases as distance increases
Figure 7 on page 354.
The larger the distance between two objects, the weaker the gravitational force

8. Free Fall When gravity is the only force acting on an object
Free fall acceleration results from gravity
g = 9.8 m/s2
For our purposes, near Earth’s surface all objects accelerate at the same rate which is 9.8 m/s2.

9. Weight The force on an object due to gravity
Weight = mass x free-fall acceleration
W = mg
Remember g is a constant, g = 9.8 m/s2
So, w = m x 9.8 m/s2
Weight is labeled as newtons (N).

10. Weight versus Mass Weight
The gravitational force an object experiences because of its mass
Depends on gravity
Mass
A measure of the amount of matter in an object
Mass remains the same regardless of gravity

11. Find the weight of a 58 kg person on the following planets:
Earth, where g = 9.8 m/s2
Venus, where g = 8.9 m/s2
Mars, where g = 3.7 m/s2
Neptune, where g = 11.0 m/s2

12. Weight influences shape
Land animals have strong skeletons to support their mass against the force of gravity.
For organisms in water, the downward force of gravity is balanced by the upward force of the water, therefore strong skeletons are not necessary.