1. Gravity ISCI 2002

2. More Free Fall

3. Free Fall Vertical and Horizontal Components of Free Fall

4. Problem A ball is thrown horizontally at 25 meters per second from a roof that is 15 meters high. How far does it travel before hitting the ground? – What do you want to know? Distance – What do you know? V x ; Roof Height – What information do you not have? Time Equations: – D = ½ at 2 – V = d/t

5. Gravity What is Gravity? – All objects pull on each other – “Gravitational Force” Gravitation force is proportional to the mass of an object Moon and Earth – Pull on each other – Earth ‘Wobbles’ – Force is the same in both directions F gravity α (m Earth ) (m Moon )

6. Mass and Gravity

7. Gravity Force inversely related to the square of the distance from Earth to the object – F gravity = 1/d 2 What happens to the force of gravity when: – Mass is constant Distance doubles? Distance reduced by ½ between the objects? – Distance is constant Mass is doubled for both objects? Mass is reduced by ½ for both objects? Inverse-Square Law – The intensity/gravity decreases as the inverse square of the distance. Gravitation Force ~ 1/d 2

8. Inverse Square Law

9. Gravity and Distance

10. Universal Law of Gravitation F = G(m 1 x m 2 ) _________ d 2 G is the “Universal Gravitational Constant” – 6.67 x 10 -11 (N x m 2 )/kg 2 – Gravitational force measured between two 1-kg objects Gravitational effects- small objects – Very small – Significant Gravitational force Large objects!

11. What does it mean to be Weightless? Weight = (m)(g) If zero acceleration, no weight! – No support force Falling elevator with scales! Astronauts in space – All things are falling at the same rate – Including the shuttle

12. Centripetal Force Objects that travel in circular path – Accelerated (directional change) – Velocity is constant Acceleration – Centripetal – Maintained - constant force exerted on object – Force (perpendicular to the velocity as the direction of the velocity changes) – Force - directed towards the center of the circle Applications – Car (CF supplied by friction of road against front tires) – Satellite (CF is Earth’s gravity pulling it toward center, perpendicular to satellite’s velocity)

13. Centripetal Force

14. Objects in Free Fall around the Earth Satellites, Space Labs, Moon – All are in free fall! Horizontal velocity = curvature of the Earth 8000m Earth drops 5 m (tangent to the surface) – 8 km/s or 29,000 km/hr or 18,000 mi/hr Rockets last stage – satellite placed in horizontal path-projection – If velocity correct, follow curvature of Earth – Launched high into the atmosphere? Why?

15. Satellite Orbits In B a circular orbit is maintained. Speed must equal 8 km/s.

16. Planets Stay in Elliptical Orbits