Unit 1: MOTION & ITS APPLICATIONS  Motion in Our Lives (P .6-7) SPH4C COLLEGE PHYSICS Unit 1: MOTION & ITS APPLICATIONS  Motion in Our Lives (P .6-7)

Motion Everything in our universe is in a state of motion. Our solar system moves through space. Earth revolves around the Sun while rotating about its own axis. People, animals, air, and countless other objects move about on Earth’s surface. The elementary particles that make up all matter, too, are constantly in motion. Scientists call the study of motion kinematics.

Motion NOTE! 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

motion Motion 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 of the objects is moving.

motion MOTION movement of an object from one place to another, as measured by an observer two objects are in motion wrt each other if the straight-line segment between them changes in: • length • direction • or both

motion PRACTICE 1. How can you tell if one object is in motion with reference to another? if the straight line segment between the object and the observer changes in length, direction, or both

motion PRACTICE 2. 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

motion PRACTICE 3. 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)

motion Uniform 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 or 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

MOTION PRACTICE 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

MOTION PRACTICE 4. 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

MOTION PRACTICE 4. 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

MOTION PRACTICE 4. 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 INTERVALS Time 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 Intervals NOTE! 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 pulled 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 intervals PRACTICE 5. What type of motion is depicted by each ticker-tape below? (a) uniform motion – the distance between the dots is constant

Measuring time intervals PRACTICE 5. What type of motion is depicted by each ticker-tape below? (b) nonuniform motion – the distance between the dots is increasing