# 8th Grade Investigations 5-8 Force and Motion

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8th Grade Investigations 5-8 Force and Motion

Unit 1: Acceleration Velocity
When physicists thing about how fast an object moves, they study how far it moves in a length of time (speed) and the direction it travels. Velocity: the change of position per unit of time.

Unit 1: Acceleration Velocity Equation
v = x t

Unit 1: Acceleration Displacement Review
t is displacement (xf - xi) Displacement can be positive or negative. Travel toward a destination is positive displacement; travel back toward the starting position is negative displacement. The displacement at the end of a walk can be zero for this reason.

Unit 1: Acceleration Acceleration
When we say something is changing velocity we say it is accelerating. Acceleration: is a change of velocity per unit of time. It is represented by a lowercase a.

Unit 1: Acceleration Acceleration
The unit of acceleration is change of position per unit of time. Velocity is measured as meters per second. v = m/s. Acceleration is measured as a = m/s/s.

Unit 1: Acceleration Acceleration
Acceleration can be positive or negative. Going faster: When an object is moving in a positive direction, positive acceleration results in increased velocity. Going Slower: When an object is moving in a negative direction, negative acceleration results in a reduction of speed.

Unit 1: Acceleration Acceleration
Acceleration is a change of velocity over time.

Unit 1: Acceleration Acceleration
At what point during a roller coaster ride is the coaster moving the fastest? B C F A G D E H

Unit 1: Acceleration Acceleration
Answer: The roller coaster is fastest at position D. This is the bottom of the longest descent, so the coaster has had the longest time to accelerate. (Refer to The Other Great Race)

Unit 1: Acceleration Acceleration
If you dropped a grape from a bridge, at what point would it be traveling at its greatest velocity? Why do you think so?

Unit 1: Acceleration Acceleration
Answer: The grape would be traveling the fastest just as it hit the water (or ground) because objects in free fall accelerate all the way down (or until they reach terminal velocity. Terminal velocity is the point at which the force of gravity is opposed by an equal force due to air resistance. (Refer to The Other Great Race)