1. Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine tomburbine@astro.umass.edu

2. What keeps the planets orbiting around the Sun?

3. Inertia - Resistance of any physical object to a change in its state of motion or rest Gravity – Attractive Force The inertia of each planet is offset by the sun's gravity The result is stable orbits around the sun

4. Aristotle (384-322 BC) Divided motion into two classes: –Natural motion – dealt with the nature of bodies (smoke rises, heavy things fall) –Violent motion – something was pushed or pulled

5. Heavy things fall faster than light things Moving objects had forces on them to keep them moving

6. Galileo’s (1564-1642) Leaning Tower of Pisa experiment Dropped things of different weights Except for air resistance, things fall at the same rate http://www.youtube.com/watch?v=gtdiHDxh3LU

7. Inertia Inertia – property by which objects resist changes in motion

8. Exercise

9. Mass Mass – quantity of matter in an object (measure of inertia) Use kilograms or grams

10. Horizontal and vertical Horizontal is sideways Vertical is up and down

11. Force Push or pull Force is given in units of Newtons

12. Equilibrium Mechanical equilibrium – Net force on an object is zero

13. Weight Weight – Force due to gravity on an object Your weight on the Moon will be 1/6 your weight on Earth http://www.youtube.com/watch?v=16D0hmLt-S0

14. Friction Friction - resistive force that opposes motion or attempted motion of an object past another with which it is in contact Always acts in opposite direction of motion

15. Support Force Weight of the book acts downwards Support (or normal) force acts upwards Sum of the forces is equal

16. Net Force Net Force is the combination of all the forces on a body http://www.dynamicscience.com.au/tester/solutio ns/flight/rocketactivitynetforce.gifhttp://www.dynamicscience.com.au/tester/solutio ns/flight/rocketactivitynetforce.gif

17. Net Force If the net force on an object is zero, the object has a constant speed

18. Exercise

19. Friction Static Friction - the friction between 2 things that aren't moving Dynamic friction - the friction between 2 moving objects

20. Speed Speed = distance/time

21. Velocity Velocity is a description of how fast something is going and in what direction

22. Acceleration Acceleration = change in velocity/time interval For example, Acceleration = (10 m/s)/(5 s) Acceleration = 2 m/s 2

23. Net Force If the net force on an object is increasing, the object is increasing in speed (accelerating) If the net force on an object is decreasing, the object is decreasing in speed (decelerating)

24. Earth’s Gravity As something falls, it increases speed The acceleration of gravity on Earth is 9.8 m/s 2

25. Homework

26. Any Questions?