1. Unit 4 – Lecture 2

2. Acceleration Acceleration – the rate of change of velocity change in velocity over a change in time a acceleration t f - t i change in time v f - v i change in velocity a = v f - v i t f - i i

3. Change represented by the Greek letter delta: Δ equals the final condition minus the initial condition example: ∆v = change in speed equation for change: v final – v initial or… v f - v i ∆

4. Acceleration – cont’d Acceleration – the rate of change of velocity change in velocity over a change in time a acceleration ∆ t change in time ∆v change in velocity a = ∆v ∆ t

5. Acceleration – cont’d Units for acceleration: unit of distance / [unit of time] 2 explanation: if unit for velocity: m/s if change in time measured in seconds = s unit = (m/s)/s = m/s 2 for every second that passes, the object will accelerate this number of meters per second

6. Acceleration – cont’d

7. In physics, acceleration is not only an increase, but also a decrease in velocity. Two ways to accelerate: change speed speed up positive acceleration slow down negative acceleration

8. Acceleration – cont’d In physics, acceleration is not only an increase, but also a decrease in velocity. Two ways to accelerate: change direction you can feel this acceleration as you turn a corner in a car – your body is being “pushed” toward the outside of the curve Acceleration can also be negative [deceleration] depending on the change in frame of reference

9. Acceleration – cont’d

10. Practice Which has the greater acceleration, an airplane that goes from 1000 km/h to 1005 km/h in 10 s, or a skateboard that goes from 0 to 5 km/h in 1 sec? What is the acceleration of a race car that whizzes past you at a constant velocity 400 km/h? If you’re running at 12 m/s and you accelerate at 0.33 m/s for 6 s, how fast are you going?

11. Gravity Gravity – the attraction of one mass toward another depends on the masses of each and their distance from one another from our perspective… gravity is a constant acceleration toward the center of the earth

12. Gravity Gravity – the attraction of one mass toward another decreases over distance explains why the moon has more of a gravitational effect [tides, etc] on the earth than the sun

13. Gravity – cont’d Galileo Galilei experimented to find out the acceleration of free- falling objects showed that free-fall was constant had difficulty showing this before using inclined planes plane reduced force of gravity & increased distance, but with same result

14. Acceleration on Galileo’s Inclined Planes Galileo found greater accelerations for steeper inclines. The ball attains max acceleration when the incline is tipped vertically.

15. Air Resistance Air resistance – the friction of air particles on an object moving through it accounts for varying speeds of falling objects

16. Air Resistance – cont’d Without air resistance, all objects fall with the same constant acceleration due to gravity

17. Recap Galileo’s Observations: a ball rolling down an inclined plane is moving with constant acceleration greater accelerations for steeper planes, max acceleration when incline is tipped vertically regardless of weight and size, when air resistance is small enough to be neglected, all objects fall with the same unchanging acceleration

18. Gravity – cont’d g = acceleration due to gravity g = 9.8 m/s 2 on earth g will change if the object gets farther away from the center of the earth [distance change] the object’s mass changes [but not in relation to the earth]

19. Practice Which of the following (if any) could not be considered an “accelerator” in an automobile: gas pedal, brake pedal, steering wheel? A sports car accelerates from 65 mph to 75 mph in 2 seconds while a minivan accelerates from 20 mph to 35 mph in 2 seconds. which has the greater acceleration? [end]