Presentation Transcript

1. Gravity And The Four Universal Forces

2. What is Gravity? Gravity: Attraction force between all objects in the universe Newton’s Universal Law of Gravitation: Every object in the universe exerts a gravitational attraction on all other objects in the universe In other words . . . Every object in the universe pulls on every other object in the universe.

3. What is Gravity? The amount of gravitational force between two objects depends upon the mass of the objects and the distance between them Fg = Gm1m2/d2 m1 = mass of object 1 m2 = mass of object 2 Fg = gravitational force G = gravitational constant d = distance between objects

4. What is Gravity? What does [Fg = Gm1m2/d2] mean? The greater the masses of the objects, the greater the gravitational force The greater the distance between the objects, the weaker the gravitational force Notice: no mention of acceleration!

5. What is Gravity? On earth, acceleration due to gravity = 9.8 m/s2 What does this mean about how fast objects fall? All objects accelerate towards earth at the same rate. See?

6. What is Weight? Weight measures the gravitational force between two objects If the mass of either object changes, weight changes See?

7. What is Weight? Because it is a force, weight is measured in Newtons (N) Remember: W = mg Practice 1. What is the weight of an astronaut with a mass of 380 pounds on earth? 2. What is the weight of the same astronaut on the moon? Hint: the moon’s gravity is 1/6th as strong as earth’s.

8. Weightlessness Appearing to be free of earth’s gravity

9. Free Fall (Weightlessness) • As long as an object is free falling, nothing exerts an upward force • If there is no upward force, Weight = 0 N

10. Gravity on Other Planets The acceleration of Gravity on other planets changes based on the mass of the planet. - The moon: 1.62 m/s2 - Mars: 3.73 m/s2 - Jupiter: 26.7 m/s2 - Venus: 8.87 m/s2 - Pluto: 0.42 m/s2 Calculate the weight of a 73 kg person on each object

11. Gravity Review 1. Attraction force between all objects 2. Weakest force in universe, but farthest range 3. Increases as the masses of the objects increases 4. Decreases as the distance between the objects increases 5. Acceleration from gravity on earth (g) = 9.8 m/s2 6. All objects fall with same g on the same planet 7. Weight is a force, not a mass

12. Four Universal Forces Gravity - Attraction based on mass Strong Nuclear Force - Holds the protons in the nucleus together and keeps electrons out Weak Nuclear Force - Allows nuclear decay to happen Electromagnetic Force – Makes positives and negatives attract and repel

13. Quiz • How does the gravity on the moon compare to the gravity on Earth? • Why don’t you notice your own gravitational pull on the Earth? • On what two things does the force of gravity depend?