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Velocity and Speed

Velocity and Speed. Mechanics. Branch of physics that studies motion Two parts Kinematics – describes motion Dynamics – tells why motion occurs. Kinematics. Translational Motion – motion without rotation All measurements must be made with respect to a frame of reference

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Velocity and Speed

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  1. Velocity and Speed

  2. Mechanics • Branch of physics that studies motion • Two parts Kinematics – describes motion Dynamics – tells why motion occurs

  3. Kinematics • Translational Motion – motion without rotation • All measurements must be made with respect to a frame of reference • A man walks at 5 km/hr toward the front of a train traveling at 80 km/hr. What is the speed with respect to a) another passenger on the train b) a person standing outside the train? • Unless otherwise stated the frame of reference is the earth

  4. Vector • Even distances need reference points • Need to say how many km from what point • Vector is a quantity that shows both a magnitude (amount) and a direction • Represented by an arrow • Scalar is a quantity that shows amount but not direction

  5. Displacement vs Distance • Displacement of an object is defined as a change in position – it is a vector • Distance is not a vector • A person walks 70m east and then turns around and walks 30m west a) what is the total distance traveled b) what is the displacement

  6. Equation • Displacement is the the ending position minus the starting position Δx = x2 - x1 • A person starts at the +30 km mark and then walks to the +10 km mark, what is their displacement

  7. Velocity vs Speed • Velocity is a vector, speed a scalar • Average speed – total distance divided by time • Average velocity – total displacement divided by time • Speed and velocity may or may not have the same magnitude

  8. Example • A person walks 70 m (E), then 30 m (W) in 70 sec. Find his a) speed b) velocity

  9. Velocity Equation • v = Δx/ Δt • If v is +, moving to the right • If v is - , moving to the left

  10. Examples • During a 3.00 s time interval a runners position changes from 50.0m to 30.5m. What is the average velocity over this time? • How far can a cyclist travel in 2.5 hr along a straight road if her average velocity is 18km/hr?

  11. Practice • A girl throws a ball 10m straight up from the top of a building that is 30m tall. A) What is the total distance the ball travels. B) What is the balls displacement • If it took the ball in the last problem 5.8 sec to hit the ground what is the A) speed B) velocity • A person drives 25 km/h for 15 minutes. How far did they go?

  12. 4) A man runs half the distance of a circular track (of radius 15 m) in 1.0 minutes. What is his a) distance traveled b) displacement c) speed d) velocity

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