Physics Section 2.1 Describe motion in terms of frames of reference, displacement and graphs An object that changes its position is said to have a displacement. A displacement is a change in position in a particular direction. displacement Δx = x f – x i Δx = displacement (m) x i = initial position x f = final position ∆x = 7 cm – 2 cm = 5 cm right A frame of reference is a system for specifying the precise location of objects in space and time. An object is at rest (not moving) if its position does not change with respect to a fixed frame of reference.

Difference between velocity and speed average velocity v av = Δx = displacement = x f – x i Δt time t f – t i v av = average velocity (m/s) Δt = change in time average speed = distance (no direction) time

Practice problems 1.Presley walks with an average velocity of.98 m/s eastward. If it takes her 34 minutes to walk to the store, what is her displacement? 2. Eric drives his car with an average velocity of 48.0 km/h to the east. How long will it take him to drive 144 km on a straight highway?

Velocity Graphs The slope of the position-time graph is the velocity. The instantaneous velocity is the slope of the line tangent to the curve at a specific point. (time) Constant velocity Variable velocity

assignment Page 47 Problems 1 - 6