2. Measuring motion Two fundamental components: Change in position Change in time Three important combinations of length and time: 1.Speed 2.Velocity 3.Acceleration

3. Description of Motion instantaneous speed - the speed that something has at any one instance

4. Units of speed miles/hour…………….mph kilometer/hour……….km/h meters/second……….m/s

5. Converting Units Converting feet to meters: 1 m = 3.281 ft (this is a conversion factor) Or: 1 = 1 m / 3.281 ft 316 ft × (1 m / 3.281 ft) = 96.3 m Note that the units cancel properly – this is the key to using the conversion factor correctly!

6. Average Speed The average speed is defined as the distance traveled divided by the time the trip took: Average speed = distance / elapsed time Is the average speed of the red car 40.0 mi/h, more than 40.0 mi/h, or less than 40.0 mi/h?

7. Velocity = {speed with a direction} Examples: 70 mph is a speed. 70 mph North is a velocity. Velocity

8. Velocity Describes speed (How fast is it going?) and direction (Where is it going?) Graphical representation of vectors: length = magnitude; arrowheads = direction

9. Acceleration Rate at which motion changes over time Speed can change Direction can change Both speed and direction can change

10. Forces - historical background Aristotle Heavier objects fall faster Objects moving horizontally require continuously applied force Relied on thinking alone Galileo and Newton All objects fall at the same rate No force required for uniform horizontal motion Reasoning based upon measurements

11. KINEMATICSDYNAMICS Description Position Velocity Acceleration Applications Horizontal motion on land Falling objects Compound (2-D) motion Explanation Forces Newton’s laws Applications Momentum Circular motion Newton’s law of gravitation

12. Aristotle on Motion (350 BC) Aristotle attempted to understand motion by classifying motion as either (a) natural motion forces acting at a distance (b) or violent motion contact forces

13. “Large object tend to 'strive harder'.” He stated that “The Earth remains at rest.”

14. Geocentric Model - Earth Centered Universe

15. Copernicus (1500's) "The Earth and planets orbit the Sun.” He reasoned this from his astronomical observations.

16. Galileo (1600's) Scientist who supported Copernicus Dropped objects with different weights from the Leaning Tower of Pisa Found that all objects fall at the same rate if you can account for air resistance http://www.youtube.com/watch?v=YD6JYdKxRjo Pisa http://www.youtube.com/watch?v=YD6JYdKxRjo http://www.youtube.com/watch?v=x7dUgiKzLSc Pisa http://www.youtube.com/watch?v=x7dUgiKzLSc http://www.youtube.com/watch?v=WOvwwO-l4ps Moon http://www.youtube.com/watch?v=WOvwwO-l4ps

17. Free fall is a state of falling free from air resistance and other forces except gravity. Free Fall

18. Galileo’s Incline Planes

19. Isaac Newton (1642-1727) His three laws of motion first appeared in his book called Principia.

20. Newton’s First Law a.k.a “Law of Inertia” A body remains at rest or moves in a straight line at a constant speed unless acted upon by an unbalanced force.

21. 10 N NET FORCE A force or a combination of forces produces changes in motion (accelerations). 10 N m = 20 N m 10 N m = 0 N m 10 N m 20 N = m

22. Scales pushing up Weight down SUPPORT FORCE A table can supply an upward support force also known as a normal force. When we say “normal to” we are saying “at right angles to”. Normal up Weight down

23. THE EQUILIBRIUM RULE Examples of Mechanical Equilibrium: Hanging from a tree Weighing yourself on a set of scales Computer setting on a table Car parked on an incline Normal up Weight down Scales pushing up Tree pulling up Normal Friction

24. The Equilibrium Rule

25. Equilibrium is a state of no change. If an object moves in a straight line with no change in speed, it is in equilibrium. EQUILIBRIUM OF MOVING THINGS Examples: Driving at constant velocity Force from road Air Resistance Normal up Weight down Terminal velocity in parachuting Weight down Air resistance

26. It is hard to detect the motion of the earth because we are moving with it. Early science could not predict large enough forces to move the earth. Can Hewitt’s bird drop down and catch the worm if the Earth moves at 30 km/s? THE MOVING EARTH

27. If an object weighs 10 lb, what must the air resistance force be if the object is falling and has reached terminal velocity? (a) 10 lb (b) 32 lb (c) there is no way of telling without knowing what the value of the terminal velocity is

28. Newton's concept of motion said that the natural state of an object was (a) constant velocity (b) constant acceleration (c) constant net force