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.