Chapter 9: Uniform Rectilinear Motion

Types of MotionRectilinear: Motion in a

straight line path. E.g. an elevator.

Curvilinear: Motion in a curved path. A ball being thrown.

Random: A combination of the above. A leaf in the wind.

Distance and Displacement Distance travelled depends on position. Distance is a scalar quantity. It is always positive. E.g. d = 5 km

Vector Diagrams

Activity Page 207, Q1. Orally, Q. 2-5, on paper

Uniform Motion The simplest motion is straight line motion in a

specific direction at a constant speed. When both speed and direction remain the same, it

is called uniform motion. Speed is a scalar quantity, = distance/time. Velocity is the vector quantity denoting speed and

direction. Velocity is the displacement of an object per unit of

time. V = Δd/Δt, Δd - displacement, Δt – time interval.

Random Motion The motion of these particles are

random because their speed and direction change.

This is an example of the Kinetic Molecular Theory (Chemistry).

Graphing Distance-Time Time is independent and on the x-axis. Distance depends on time and is on the

y-axis. The slope of the graph gives us the

speed. If it was a displacement-time graph,

slope would give the velocity.

Activity Page 209. Q 1 - 3

Lab Experiment – Can You Walk in a Uniform Way – Ticker Tape

Graphing Velocity Velocity is considered to be dependent

on time. Average velocity = total displacement

total time av = Δd/Δtע

Average Velocity & Speed This is done by taking the slope of a line

at two different points. Average velocity = ∆ displacement

∆ time Unit = m/s [direction] Average speed = ∆ distance

∆ time Unit = m/s

Average Velocity: Uniform Acceleration Average Velocity during uniform

acceleration can be calculated by taking the mean of 2 velocities.

vavg = v2 + v1

2P. 209, Q 1-3

Distance & Speed We already know that speed = distance time So distance = speed x time Distance can be determined by the area

under the curve of a velocity-time graph.

Exam Question What is the displacement after 25 s?

20

15

10

5

0

-5

-10

-15Time (s)

Velocity (m/s)

0 5 10 15 20 25 30

Activity Page 213, Q. 1-5 Page 215, Q 1-4

Summary Some motions can be seen easily; other

motions must be observed using other senses or devices.

The trajectory is the path of a moving object.