Teacher Page IV. Force, motion and mechanical energy A. Relative Motion 7th grade assessment Science standards 3.1; 3.3; 4.1 Students should be able to explain how an object’s acceleration is affected by outside forces and its mass. View lesson before using with students. Click mouse to view sample questions and answers.

What is acceleration? Increasing speed. Decreasing speed. Changing direction.

In your journal describe the acceleration of a race car as it runs the race course. Increasing speed - When the car begins to move from a stopped position or speeds up to pass another car. Decreasing speed - When the car stops at the pit or slows down for a yellow flag. Changing direction - When the car enters a curve or changes lanes.

Calculating Acceleration A roller coaster picks up speed as it rolls down the slope, its speed is 4 m/s. But 3 seconds later, at the bottom its speed is 22 m/s. What is its average acceleration? Analyze: You know the initial velocity and final velocity of the car, and the length of time during which its velocity changed. You are looking for its acceleration. Write the formula: Acceleration = Final velocity - Initial velocity Time

Calculating Acceleration A roller coaster picks up speed as it rolls down the slope, its speed is 4 m/s. But 3 seconds later, at the bottom its speed is 22 m/s. What is its average acceleration? Substitute and solve: Acceleration = 22 m/s - 4 m/s 3 s Acceleration = 18 m/s = 6 m/s 2 3 s

Practice Problem An eagle accelerates from 15 m/s to 22 m/s in 4 seconds. What is the eagle’s average acceleration? Acceleration = 22 m/s - 15 m/s 4 s Acceleration =