Bellringer January 30 th 2013 If an astronaut

Bellringer � January 30 th 2013 �If an astronaut throws a ball in space, when will the ball stop? � WRITE THE QUESTION AND ANSWER.

Speed, Velocity, & Acceleration

What is speed? � Speed is a measure of how fast something moves or the distance it moves, in a given amount of time. The greater the speed an object has, the faster it changes position.

Review � The rate at which an object moves is its speed. Speed can be calculated this way: › Speed = Distance/Time S

Example �A train travels 300 km in 5 hours. Solve to find the train’s speed. S

Speed Word Problems �A bug crawled 25. 0 cm in 5. 0 seconds. Its average speed was ______. � In 2. 5 seconds, a turtle was able to travel 10. 0 cm. Its average speed was _______.

Speed, Velocity, & Acceleration 1. What is velocity? � Velocity is a speed in a specific direction. 2. What is acceleration? � The rate at which velocity changes with time. 3. What is the relationship between velocity and acceleration? � Acceleration is a measure of how quickly the velocity changes. If velocity does not change, there is no acceleration.

Definition of Acceleration § An acceleration is the change in velocity per unit of time. § A change in velocity requires the application of a push or pull (force). A formal treatment of force and acceleration will be given later. For now, you should know that: • The direction of accel- eration is same as direction of force. • The acceleration is proportional to the magnitude of the force.

ACCELERATION Acceleration includes: a) Speeding up; also called accelerating or positive acceleration.

ACCELERATION b) Slowing down; also called decelerating or negative acceleration.

ACCELERATION c) Turning, which is a change of direction.

Acceleration and Force F a 2 F 2 a Pulling the wagon with twice the force produces twice the acceleration and acceleration is in direction of force.

ACCELERATION The formula to calculate acceleration is: (Final velocity) – (Starting velocity) The amount of time the change takes “Change” = Vf – V i t = ΔV t

ACCELERATION * The SI unit for acceleration is: m/s/s or m/s 2 ** This is because you are dividing velocity (m/s) by time (s)

Example of Acceleration + Force t=3 s v 0 = +2 m/s vf = +8 m/s The wind changes the speed of a boat from 2 m/s to 8 m/s in 3 s. Each second the speed changes by 2 m/s. Wind force is constant, thus acceleration is constant.

� Acceleration is positive (+) or negative (-) based on the direction of force. � Positive acceleration is speeding up. � Negative acceleration is slowing down.

ACCELERATION 7. Parachute example: A man jumps from a plane. His beginning speed is 100 mi/hr, and his ending speed with his parachute is 10 mi/hr. This took 3 sec. What was his acceleration? (10 mi/hr – 100 mi/hr) = -30 mi/hr/s The negative sign means 3 s that he was decelerating (slowing down).