Introduction to MotionSPH4C – Unit #1 Kinematics

Big Ideas

Concepts that students should retain after this course are:

• All motion involves a change in the position of an object over time.

• Motion can be described using mathematical relationships.

• Many technologies that apply concepts related to kinematics have societal and environmental implications.

Overall ExpectationsBy the end of this unit, students will…

1. Analyze selected technologies that are used to move objects or track their motion, and evaluate their impact on society and the environment, including their contribution to scientific knowledge.

2. Investigate, in qualitative and quantitative terms, the linear uniform and non-uniform motion of objects, and solve related problems.

3. Demonstrate an understanding of different kinds of motion and the relationships between speed, acceleration, displacement and distance.

Motion Learning Goals

After this topic I will be able to…

• Define kinematics, motion (uniform and non-uniform)

• Describe the differences between uniform and non-uniform motion

MotionWhat is the physics of motion all about? Motion is part of the physical world. We learn to walk, run, and drive without understanding the physics of motion. We do, however, have an idea of motion and its effects and causes.

MotionEverything in our universe is in a state of motion. Our planet moves around our sun along with other objects and planets in our solar system. Our solar system moves around our galaxy the Milky Way located within a universe of countless other galaxies which are all moving. People, air, animals, and countless other objects that make up our planet all move about the Earth’s surface. The elementary particles that make up all matter in the universe, too, are in constant motion. Scientists call the study of motion kinematics.

Kinematics: the study of motion.

MotionNote:To understand the motion of objects, we must first be able to describe motion. Physicists use a number of specific terms and units to describe motion. You are likely already familiar with many of these terms and units – distance, speed, velocity, acceleration, …

Kinematics:• The study of motion.

MotionMotion is defined as the movement of an object from one place to another, as measured by an observer. But what is the observer measuring? Consider two objects connected by a straight line segment. If the straight line segment between them changes in length, direction, or both, one or both the objects is moving.

MotionMotion• Movement of an object from one place to another, as

measured by an observer• Two objects are in motion with respect to (wrt) each other if

the straight-line segment between them changes in:• Direction• Length• Both

MotionPractice1. Two golf carts are travelling at the same speed in the same

direction along a straight level path. Are the carts in motion with reference to each other? Explain.

No – the straight line segment between the two golf carts does not change in length or direction.

MotionPractice2. The engine of a freight train is pulling five cars around a

gradual curve. Is the engine in motion with reference to the last car? Explain.

Yes – the straight line segment between the engine and the last car changes in direction (the length stays relatively constant though).

MotionUniform motion is a movement at a constant speed in a straight line. However, most motion in our lives are classified as non-uniform, which means the movement involves changes in speed, direction, or both. A roller coaster is an obvious example of such motion – it speeds up, slows down, falls, and travels around corners.

Uniform Motion• Movement at a constant speed in a constant direction

Non-Uniform Motion• Movement that involves changes in speed or direction or both

MotionPractice3. Are the motions described below uniform or non-uniform?

Explain.a) A rubber stopper is dropped from your raised hand to the

floor.

(a) Non-uniform – the speed is changing.

MotionPractice3. Are the motions described below uniform or non-uniform?

Explain.b) A car is travelling at a steady rate of 85 km/h due west.

(b) Uniform – the speed and direction are constant

MotionPractice3. Are the motions described below uniform or non-uniform?

Explain.c) A motorcycle rider applies the brakes to come to a stop.

(c) Non-uniform – the speed is changing

MotionPractice3. Are the motions described below uniform or non-uniform?

Explain.d) A race car travels around a circular track at a constant

speed.

(d) Non-uniform – the direction is changing

Measuring Time IntervalsTime is an important quantity in the study of motion. In physics classrooms, various instruments are used to measure intervals of time including:

• A digital timer

• A computer with sensors attached

• Ticker-tape timers

Measuring Time IntervalsNote:A ticker-tape timer has a metal arm that vibrates at constant time intervals. A needle on the arm strikes a piece of carbon paper and records dots on a paper tape through the timer. The dots give a record of how fast the paper tape is pulled. The faster the motion, the greater the spaces between the dots. Most ticker-tape timers vibrate at 60 Hz which means that they make 60 dots on the paper each second (so each dot interval represents 1/60 s). The tape is then separated into 6-dot intervals which represent 1/10 s or 0.10 s intervals.

Measuring Time IntervalsPractice4. What type of motion is depicted by each ticker-tape below?

a) _

(a) Uniform motion – the distance between the dots is constant.

Measuring Time IntervalsPractice4. What type of motion is depicted by each ticker-tape below?

b) _

(b) Non-uniform motion – the distance between the dots is changing

Activity

Complete the Activity 1.2 In your textbook. Record your results in your notebook.