Chapter 2—Motion Chapter 2—Motion in One Dimensionin One Dimension

Section 1: Displacement and Velocity

DistanceDistance—the total path-—the total path-length traveled by an length traveled by an object; add-up each leg of object; add-up each leg of the trip.the trip.

Units: meters, feet, km, cm, inches, miles, light-years

Symbol: dScalar Quantity—a quantity that has magnitude (size) only; no direction. Examples: distance, speed, mass, density, time, energy

Example of Distance:Example of Distance:

A = 50 mB = 45 mC = 40 m

A + B = 95 m

DisplacementDisplacement——the straight-the straight-line distance between two line distance between two points, along with direction.points, along with direction.

Units: SAME AS FOR DISTANCESymbol: xVector Quantity—a quantity that has both magnitude and direction.Examples: displacement, velocity, acceleration, force, momentum.

Example of Displacement:Example of Displacement:

A = 50 mB = 45 mC = 40 m

C = 40 m, north

SpeedSpeed——the rate at which a the rate at which a distance is traveled.distance is traveled.

◦Units: m/s, mi/hr, km/hr, cm/s, ft/min, mi/day

◦Symbol: s◦Scalar Quantity◦Instantaneous speed: an object’s rate of travel at a particular instant in time

◦Average Speed—the total distance traveled divided by the total time of travel.t

ds

Example ProblemExample Problem: A car travels 120 : A car travels 120 km at 60km/hr. It then turns around km at 60km/hr. It then turns around and returns to its starting point at 30 and returns to its starting point at 30 km/hr. What was its average speed km/hr. What was its average speed for the entire trip?for the entire trip?d1 = 120 km d2 = 120 km

s1 = 60 km/hr s2 = 30 km/hr

t1 = d1/s1 t2 = d2/s2

t1 = 120 km/60 km/hr t2 = 120 km/30 km/hr

t1 = 2 hrs t2 = 4 hrs

s = dtot/ttot

s = 240 km/6 hrss = 40 km/hr

You will absolutely, guaranteed, see a

problem just like this one again on future tests!

VelocityVelocity——the rate of the rate of change in an object’s change in an object’s displacementdisplacement

◦Units: SAME AS FOR SPEED◦Symbol: v◦Vector Quantity◦Average Velocity—total displacement divided by total time of travel.

 

Note: If an object changes direction during its motion, its speed will be _______ the magnitude of its velocity. If an object does not change direction during its motion, its speed will be _______ the magnitude of its velocity.Can you explain why this is

so?