Change in Velocity

• Each time you take a step you are changing the velocity of your body.

• You are probably most familiar with the velocity changes of a moving bus or car.

• The rate at which velocity (speed or direction) changes occur is called acceleration.

Acceleration= final velocity- starting velocity time

Change in velocity = final – starting

velocity velocity Acceleration= change in velocity

time

Acceleration =Velocity(final) - Velocity(original)

time

A car traveling at 60 mph accelerates to90 mph in 3 seconds. What is thecar’s acceleration?

=90 mph - 60 mph

3 seconds

=30 mph

3 seconds

= 10 mph/second

Positive acceleration

Negative acceleratio

n

Acceleration =Velocity(final) - Velocity(original)

time

A car traveling at 60 mph slams on the brakes to avoid hitting a deer. The car comes to a safe stop 6 seconds after applying the brakes. What is thecar’s acceleration?

=0 mph - 60 mph

6 seconds

=- 60 mph

6 seconds

= - 10 miles per hour per second

- A constant acceleration produces a straight line or

linear slope (rise/run).

- The slope of a non-linear velocity-time graph

(rise/run) will predict an objects instantaneous

acceleration.

a = v/t

Free fall• The constant acceleration of an

object moving only under the force of gravity is "g".

• The acceleration caused by gravity is 10 m/s2

• If there was no air, all objects would fall at the same speed

• Doesn’t depend on mass• After 1 second falling at 10 m/s• After 2 seconds 20 m/s• 3 seconds 30 m/s

Falling

• Air resistance will increase as it falls faster

• An upward force on the object

• Eventually gravity will balance with air resistance

• Reaches terminal velocity - highest speed reached by a falling object.

Terminal velocity• Force of gravity is constant

air resistance increases as you speed up

until the force is equal

Equal forces, no acceleration

constant velocity terminal velocity

Balloon Racers

• What will happen if I let go of the blown up balloon?

• Why did that happen?• How can we measure the speed, distance or

acceleration of the balloon?– A track?– Attach the balloon to something?