Acceleration

Bell Ringer: 9/21 What would the velocity graph look like?

2. What are the three devices on a car that can make it change its velocity?

They change the rate of speed over time What pedal is this? What pedal is this? They change the rate of speed over time

What device in your car cause it to change DIRECTION?

Bell work What is it’s acceleration?

Acceleration The rate (time) at which an object changes its velocity

Acceleration is ANY change in velocity. When you are in a car and you step on the “accelerator” the car accelerates (speeds up) POSITIVE acceleration When the brakes are applied, the car also accelerates (slows down) Negative acceleration (deceleration)

VELOCITY Speed Displacement Recall that velocity is speed AND direction VELOCITY Speed Displacement So…. If a car goes around the block at a constant speed of 30 mph, is it accelerating???

Distance & Displacement What is displacement? Change in POSITION From the initial position to final position. Where did it “end up” compared to where it started?

Galileo rolled balls down a series of ramps. As the ramps got higher, the balls rolled at a greater speed. Their speed increased. Galileo said that they were….. Accelerating.

Acceleration Units: m/s2 Acceleration occurs when an object Speeds up (+) Slows down (-) Change in direction Units: m/s2 Acceleration= Final velocity – initial velocity Time Accel = Δv t

Acceleration formula a = ∆v t a = velocityfinal – velocityinitial time ∆ “change in”

Positive & Negative Acceleration Positive acceleration “speeding up” Negative acceleration “slowing down”

Practice Problem #1 If a car starts from rest, and reaches a speed of 100 m/s north in 10 seconds, what is the acceleration? G U E S acceleration Final V – Initial V time Initial velocity = rest 0 m/s Final velocity = 100 m/s Time = 10 sec +10 m/s/s 100 m/s – 0 m/s 10 sec or +10 m/s2

Practice Problem #2 What is the acceleration when a car slows down from 100 km/hr to 60 km/hr in 5 seconds? G U E S

Practice Problem #3 What is the acceleration of a dragster that reaches a speed of 200 miles/hr in 4 seconds? G U E S

Work Sheet Work on the Acceleration worksheet with your shoulder partner

Practice Problem Describe the motion of the object at each part on the graphs. Time Velocity D E F Distance Time A B C

Bell Ringer Which of the following are the units for acceleration? (hint: more than one answer) a) m/s2 b) km/hr s c) m/s d) miles Which of the following is not accelerating? A car slowing to a stop at a stop sign You riding a Ferris Wheel The moon orbiting the Earth A cyclist riding constantly at 2 m/s on a straight path

Bell Ringer Which of the following are the units for acceleration? (hint: more than one answer) a) m/s2 b) km/hr/s c) m/s d) miles Which of the following is not accelerating? A car slowing to a stop at a stop sign You riding a Ferris Wheel The moon orbiting the Earth A cyclist riding constantly at 2 m/s on a straight path