1. Velocity & Acceleration Some Review

2. Defining Velocity Kinetic energy was –KE=1/2 (mass) (velocity) 2 We know that the mass of an object is the actual amount of matter in the object expressed in grams or kilograms.

3. Velocity Describes both the rate and direction of the motion If an object speeds up or slows down in the given direction we say there is a change in velocity

4. VELOCITY AND SPEED Velocity is a measure of how fast an object is traveling in a particular direction. OR The rate of change of an object’s position 1.Velocity changes as speed or direction changes 2.Is constant only if both its speed and direction remain the same Bus traveling 15 m/s south increases speed to 10 m/s south – speed changed – so did velocity

5. VELOCITY Velocity = distance ÷ time The units we use are m/s and d is distance. Rearranging the formulas for all possibilities: V= d/t d = vt t = d/v

6. VELOCITY What is the velocity of a car that travels 100m north in 2 hours? V = d/t 100.m/2h = 50.0m/h A car travels 65.0m/h east for 3.00 hours how far did it go? d = vt (65.0m/h) (3.00h) = 195m = How long would it take a car to travel 200 miles south at a velocity of 70m/h? t = d/v t = 200m/70m/h t = 2.9h = 3hr Make sure you work your problems so that units cancel out.

7. Speed Speed = Distance x Time 1.distance an object moves per time 2.measure of how fast an object is moving 3.Does not include a direction 4.Merry-go-round – does not move in a single direction so does not have velocity

8. ACCELERATION Acceleration is the change in velocity per unit of time. An example of this is when you travel in your car. Your velocity is not constant throughout the entire trip as you slow down and speed up as necessary. A positive acceleration means that you are speeding up and a negative acceleration means that you are slowing down.

9. ACCELERATION Acceleration has the formula: Acceleration = (Final Velocity) – (initial velocity) (Final time) – (Initial time) OR (time it takes to change velocity) A = v f – v i = ∆v∆ means “change in” t f – t i ∆ t Acceleration has the units of (distance unit)/(time unit) Ex: m/s 2 or mi/h 2

10. ACCELERATION Example acceleration problems Calculate the acceleration of an object with: »Initial Velocity : 0.0m/s »Final Velocity: 14m/s »Time 4.0s »A = 14m/s – 0.0 m/s 4.0s A = 3.5m/s 2

11. ACCELERATION A car stops from a velocity of 55m/s in 15 seconds. What is the cars acceleration? Is the car speeding up or slowing down? A = 0 – 55m/s = -55m/s 15 s 15s A = -3.7m/s 2 Car is slowing down

12. ACCELERATION A runner achieves a velocity of 21.1m/s 10.0 seconds after he begins. What is his acceleration? What distance did he cover in the 10.0 seconds? a = 21.1m/s – 0 a = 2.11m/s 2 10.0s d = v t (21.1m/s)(10.0s)= 211m

13. Examples of Acceleration ExampleHow velocity changes A plane taking offAn increase in speed A car stopping for a traffic lightA decrease in speed A person jogging on a winding trailA change in direction A person turning right at an intersection A change in direction