Coordinated Science CMonday, November 26th, 2012

Acceleration and Speed vs. Velocity

Entry TaskAt this point on the

rollercoaster ride, the monks feel like they don’t weigh anything (similar to a sky diver’s free-fall sensation.)

Why do the monks feel like they have no weight when going downhill on the rollercoaster?

Students Ideas about Entry Task:Feel weightless, you feel zero G’s (hangtime).G-amount of gravitational force.When you go down you get less G’s.When you are going down a hill, you are

going really fast.

Classwork: Rollercoaster’s change in velocityPosition Velocit

y:Change in Velocity=final velocity-initial velocity

Time: Change in Time=final time-initial time

Acceleration=change in velocity ÷ change in time

start Ex. 0 m/s

Ex. none 0 sec. None None

uphill Ex. 10 m/s

Ex. +10 m/s 5 sec. 5 sec. 2 m/s2

downhill 19.8 m/s  9.8 m/s 6 sec.  1 sec  9.8 m/s2

downhill 30 m/s  10.2 m/s 10 sec.  4 sec  2.55 m/s2

downhill 39.8 m/s  9.8 m/s 11 sec.  1 sec  9.8 m/s2

uphill 30 m/s  -9.8 m/s 12 sec.  1 sec  -9.8 m/s2

What is the acceleration due to gravity?-9.8 m/s2 (Why does the acceleration due to

gravity have a negative sign?)

Any objects that are close to earth are pulled towards the earth at 9.8 m/s2 by the force of gravity.

Physicists are still debating what causes the force of gravity, besides knowing that objects that have mass usually have a gravitational force between them.

When does the acceleration of the rollercoaster equal the acceleration due to gravity, but has the opposite sign? Look at your table.6 seconds. Why is it not equal and have the

opposite sign at 12 seconds?

How do you think you would feel when the acceleration of the rollercoaster equals the acceleration due to gravity?

The weightless feeling discussed in the Entry Task.

Design a rollercoaster that gives riders the feeling of weightlessness.

Position on the roller coaster

Velocity Change in Velocity

Time Change in Time

Acceleration

Beginning 0 m/s 0 secondsuphill 50

secondsdownhill 100

secondsuphill 150

secondsdownhill 200

secondsuphill 250 sec.downhill 300 sec.End 350 sec.

Rules for designing rollercoaster1.When going uphill at the beginning of

the ride, you will accelerate.2.When going uphill any other point, you

must decelerate.3.When going downhill, you should

accelerate.4.Draw two graphs, one showing velocity

vs. time and one showing acceleration vs. time.

5. The velocity will always be positive, because the rollercoaster will never be going in reverse. It only goes from the start towards the end.

Homework for Tonight:Page. 68 in your Active Physics Textbook:Physics To Go Questions: 1, 3-7