Describing Motion Kinematics in one Dimension

Mechanics Study of the motion of objects and the related forces and energy Kinematics –Description of how objects move Dynamics –Deals with force and why objects move Translational Motion –Motion without rotation (start with 1-d)

Reference frames Section 2.1 Its about how you look at the situation !!

Frame of reference –A measurement of position, distance or speed must be made in reference to something. Does a bug sitting on your dashboard know he’s moving? What Different frames of reference do you see?

Distance vs. Displacement Basketball at desk demo Distance- –Total amount traveled Displacement Displacement –Change in position Δx = x 2 - x 1 Ex: Start at exit 34 finish at exit 65 Ex: Start at exit 34 finish at exit 65 –Displacement = x 2 - x 1 – 65mi – 34mi = 31mi –What if you stat at exit 65 and go to 34? –Displacement = 34mi – 65mi = -31mi

Vector vs Scalar Vector quantity- –A quantity that has both magnitude and direction. –Represented in diagrams as arrows Ex: displacement Scalar quantity- –A quantity that can be described by magnitude alone Ex: distance, money

Speed vs. Velocity Average Speed - –Distance traveled/time elapsed Average Velocity- –magnitude and direction of an object’s motion If displacement is along the x- axis, use x to indicate displacement.

Try one! During a 2 minute interval a person walks from 200m away from the origin to 20m away from the origin. Calculate their average velocity in meters per second. x 1 = x 2 = t = v= x 1 = 200m x 2 =20m t =2 min v= ? x 1 = 200m x 2 =20m t =120 s v= ? v = 20m - 200m / 120 sv = -180m / 120 sv = - 1.5v = m/s

Acceleration Acceleration is the rate at which velocity changes –Change in velocity can be Speeding up OR slowing down Changing direction Acceleration = change in velocity/ time interval Acceleration is a change in speed or direction!!!!

Some details Units: –km/h*s, m/s*s = m/s 2 What does that mean???? –If something can accelerate at 5 km/h*s –If something accelerates at 10 m/s*s = 10 m/s 2 timespeed 1s5km/h 2s10km/h 3s15km/h timespeed1s 10 m/s 2 2s 20 m/s 2 3s 30 m/s 2