Kinematics Intro

Objects and Systems Classical physics studies how objects behave under different conditions An object is a piece of matter to which some sort of action (push or pull) is directed A system is any group of one or more objects we choose to study What are the parts of this system?

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 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

Vector Even distances need reference points Need to say how many km from what point - may use words like “up”, “down”, “east”, “west”, etc. 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

Example For each below indicate if it is a vector or scalar quantity: 1) 5 m 2) 30 m/s East 3) 256 bytes 4) 5 mi North 5) 20 o C above freezing 6) 4000 calories

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

Position A coordinate axis is often used to show a frame of reference from the zero point Objects right of the zero have a positive value while those to the left are negative - positive and negative signs indicate direction The position of the object is given by the x coordinate

Equation Displacement is the the ending position minus the starting position Δx = x 1 - x 0 A person starts at the +30 km mark and then walks to the +10 km mark, what is their displacement

Example Consider a football coach pacing back and forth along the sidelines. The diagram below shows several of coach's positions at various times. At each marked position, the coach makes a "U-turn" and moves in the opposite direction. In other words, the coach moves from position A to B to C to D. What is the coach’s displacement and distance of travel?