PHYSICS 103: Lecture 3 Motion under uniform acceleration Freely falling objects çAcceleration due to gravity çTracking a falling object Agenda for Today:

Description of Motion with Uniform Accleration Remember from last class that acceleration is: v = final velocity v 0 = initial velocity Where: If a is constant:

Example of Uniform Accleration: A car accelerates at 3 m/s 2 from rest. What is the final velocity after 20 seconds? We know: v 0 =0 m/sa=3 m/s 2 t=20 s How far did it travel in this time?

Remember from last class that distance is: If acceleration, a, is constant, then: If acceleration, a, is constant, then the final velocity, v, is given by: so:

Motion with Uniform Acceleration d = d 0 + v 0 t + 1 / 2 at 2 Initial distance at t = 0 acceleration Initial velocity: velocity at t = 0 v= v o + at Initial velocity: velocity at t = 0 acceleration Final velocity When an object accelerates at a constant rate the following applies:

Example Problems for Uniform Accleration: 4)A car starts out at a velocity of 2 m/s. If its acceleration is 3 m/s 2, how long will it take the car to travel 640 m? 1) A car starts out at a velocity of 2 m/s. If it's acceleration is 3 m/s 2, how fast will it be going in 20 s? 2) A car starts out at a velocity of 2 m/s. If it's acceleration is 3 m/s 2, how long will it take before it will be going 62 m/s 3) In the problem above, how far will it have traveled?

Freely falling objects 1) Heavy objects and light objects fall at the same rate with no air resistance 2) Things fall faster and faster until they hit the ground (acceleration) Observations:

Acceleration due to Gravity Free-fall is an example of motion with uniform acceleration

A ball is dropped from a a tall building. How long does it take to reach the ground? How fast is it going? initial final where h = 1224 ft = 373 m to 102 nd floor

v= v o + at d = d 0 + v 0 t + 1 / 2 at 2 d=373 md 0 =0 mv 0 =0 m/s 0 0 Example of free-fall: initial final v= v o + at = 0 + (10m/s2)(8.64s) = 86.4m/s = 86.4 m/s (1/1000 km/m)(1/1.61 mile/km)(3600 s/hr) = 193 mph

Motion with Uniform (Constant) Acceleration Main Points from Today’s Lecture Free fall d = d 0 + v 0 t + 1 / 2 at 2 Initial distance at t = 0 acceleration Initial velocity: velocity at t = 0 v= v o + at Initial velocity: velocity at t = 0 acceleration Final velocity  How long does it take to drop things  How fast are they going at any given time?

HW Re-Read Ch 3 Make sure you understand all example problems done in class