Opening Activity

Opening Activity • Compare and contrast the following: • Speed and velocity • Distance and displacement • Average speed and instantaneous speed • A cyclist must travel 800 km. How many days will the trip take if the cyclist travels 8 h/day at an average speed of 16 km/h?

3.2 Acceleration pp 76-80Essential Questions • How are time, velocity, and acceleration related? • How do I calculate the average acceleration of an object? • What is positive and negative acceleration and how are they different?

Acceleration, Speed, and Velocity p 76 • When a car takes from a stop, the car’s velocity increases. It also accelerates. • Acceleration is the change in velocity divided by the time for the change to occur

Acceleration, Speed, and Velocity p 76 • When a car slows down and stops, the car’s velocity decreases. It also accelerates (deceleration).

Changing Direction p 77 • Acceleration occurs when an object changes its speed, its direction, or both. • We now have three terms that have magnitude (size) and direction; these are vectors. Name the other two vectors we have covered

Changing Direction p 77 • Any time a moving object changes direction, its velocity changes and it is accelerating.

Calculating Acceleration • = • Standard units = m/s2 • If a = 1 m/s2, it means that its velocity (speed) is increasing 1 m/s every second.

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration?

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = _____ vf = ______ Δt = _____

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = 0 m/s vf = ______ Δt = _____

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = 0 m/s vf = 80 m/s Δt = _____

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = 0 m/s vf = 80 m/s Δt = 20 s

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = 0 m/s vf = 80 m/s Δt = 20 s • =

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = 0 m/s vf = 80 m/s Δt = 20 s • = =

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = 0 m/s vf = 80 m/s Δt = 20 s • = = =

Suppose a jet airliner starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s.What is the plane’s average acceleration? • vi = 0 m/s vf = 80 m/s Δt = 20 s • = = = = 2.0 m/s2

Now imagine that a skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 seconds. What is the skateboard’s average acceleration?

Now imagine that a skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 seconds. What is the skateboard’s average acceleration? • vi = _____ vf = _____ Δt = _____

Now imagine that a skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 seconds. What is the skateboard’s average acceleration? • vi = 3 m/s vf = 0 m/s Δt = 2 s

Now imagine that a skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 seconds. What is the skateboard’s average acceleration? • vi = 3 m/s vf = 0 m/s Δt = 2 s • =

Now imagine that a skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 seconds. What is the skateboard’s average acceleration? • vi = 3 m/s vf = 0 m/s Δt = 2 s • = =

Now imagine that a skateboarder is moving in a straight line at a constant speed of 3 m/s and comes to a stop in 2 seconds. What is the skateboard’s average acceleration? • vi = 3 m/s vf = 0 m/s Δt = 2 s • = = = = -1.5 m/s2

Opening Activity • It takes a car one minute (60 seconds) to go from a dead stop to a speed of 40 m/s. What is the average acceleration of the car? • A truck cruising at 50 m/s slams on its brakes to avoid a collision, stopping in 3.5 s. What is the acceleration of the truck

Opening Activity • It takes a car one minute (60 seconds) to go from a dead stop to a speed of 40 m/s. What is the average acceleration of the car?

Opening Activity • It takes a car one minute (60 seconds) to go from a dead stop to a speed of 40 m/s. What is the average acceleration of the car?t = 60svi = 0 m/svf = 40 m/sa = ???

Opening Activity • It takes a car one minute (60 seconds) to go from a dead stop to a speed of 40 m/s. What is the average acceleration of the car?t = 60svi = 0 m/svf = 40 m/sa = ??? = (vf – vi)/(tf – ti)=(40-0)/60 = 0.67 m/s2

Opening Activity • A truck cruising at 50 m/s slams on its brakes to avoid a collision, stopping in 3.5 s. What is the acceleration of the truck?

Opening Activity • A truck cruising at 50 m/s slams on its brakes to avoid a collision, stopping in 3.5 s. What is the acceleration of the truck?t = 3.5svi = 50 m/svf = 0 m/sa = ???

Opening Activity • A truck cruising at 50 m/s slams on its brakes to avoid a collision, stopping in 3.5 s. What is the acceleration of the truck?t = 3.5svi = 50 m/svf = 0 m/sa = ??? = (vf – vi)/(tf – ti)=(0-50)/3.5 = -14.29 m/s2

Speed-Time Graphs – Calculating Positive Acceleration • = = = = 2.0 m/s2

Speed-Time Graphs – Calculating Negative Acceleration • = = = = -1.5 m/s2

3.2 Homework • p 80 1-7 (All classes) • p 880 26-28, 30-32 (Honors)

Opening Activity