Velocity and Acceleration8SCIENCE Thurs. May 5/Fri. May 6

Review: Forces and Motion/Speed

• What is speed?– Rate of change of a position

• How do you calculate average speed?– Average speed = total distance

time

• What is displacement?– Change in position including a

direction

• What is velocity?– Rate of change of displacement

How Velocity and Acceleration are related

• Velocity provides more information by including a direction of movement

• You can sense a change in velocityExample: when a car starts driving and quickly slows down, you can feel a change in velocity - When you slow down or stop, your body may push against the seatbelt

• These changes in velocity: speeding up, slowing down and turning are all forms of acceleration

Acceleration• Acceleration is the rate of change of velocity

(speed with direction)

• Acceleration may be positive or negative:Positive – accelerates in the direction it is moving (speeds up)

• Ex: riding your bike forward and pedal harder to speed up

– Negative – accelerates in the opposite direction to its movement (slows down)• Ex: riding your bike and pushing the brake slows you

down

Positive and Negative Acceleration

POSITIVE

NEGATIVE

POSITIVE

Calculating Acceleration• Average acceleration (a) = change in velocity (v₂ - v₁)

time (t)• Usually in m/s²

Example: If a student takes 2 s (seconds) to go from velocity of 0m/s to a velocity of 4m/s, what is the average acceleration?

Example: If a car begins at a velocity of 2m/s and then speeds up to 18m/s over 4 s what is the average acceleration?

Example: What does it mean if your acceleration is 0m/s?- This means you are not moving or that you are moving at a constant speed, and not speeding up/slowing down i.e. parked car, driving at a constant rate of 60km/h

Motion: Calculating Acceleration minilab pg. 1521) Work with a partner. One of you should clap a slow, steady beat. The other partner should move

along the taped course, stepping beside each line on the piece of tape.2) You should try and step beside each piece of tape on the beat of your partner’s claps. 3) Create the table below to record information: Calculate the change in displacement (velocity)

and the change in velocity (acceleration) for each time*Remember: velocity = displacement

time

Displacement = change in position

Acceleration = final velocity – initial velocity

time

4) Experience negative acceleration by moving through the course from 3.6 – 0 while your partner claps a steady beat.QUESTION: 4) As you move through the course forward and backward, does your velocity change?

Time (t) claps

Distance (d) in meters

Velocity (v) (m/clap)

Acceleration (a) (m/clap²)

0 0

1 0.1

2 0.4

3 0.9

4 1.6

5 2.5

6 3.6