Part 1: Measuring Motion

Objectives You will be able to explain the

relationship between motion and a frame of reference

You will be able to relate speed to distance and time

You will be able to distinguish between speed and velocity

You will be able to solve problems related to time, distance, displacement, speed, and velocity

What is Motion? Motion is an object’s change in

__________ relative to a reference point.

What are some examples of motion in the world around you?

How do we know when an object is moving?

Observing Motion Is more than just observing an object You have to observe the object in relation

to a stationary object This stationary object is called a

reference point or frame ___________ is a common reference point When your objects changes position in

comparison to a reference point, then it is in motion

Using the mountain as a reference point, we can see that the balloon is in motion

We can also give reference directions such as north, south, east, west, up or down

How is the balloon moving?

Distance vs. Displacement Distance measures

the path taken by an object

It doesn’t have to be in a straight line or in a specific direction

Example:› If I walk home from

school and then come back I have covered a distance of 5 blocks in total

Displacement is the change of an object’s position

It must be in a straight line and it must have direction

Example:› If I walk home

form school and then come back , my displacement is zero towards home

Practice Problem 1 A tiger paces in her cage: first 8 ft. to

right, then 8 ft. to the left , and finally 8 ft. back to the right

What is the total distance the tiger has traveled?

What is the displacement of the tiger?

Speed You know from experience that some

objects move faster than others Speed describes how fast an object moves Speed measurements involve distance

and time So speed is measured in units of meters

per second (m/s) When an object covers equal distances in

equal amounts of time, it is moving at a _________________

Speed Continued Speed can be studied with graphs and

equations It can also be determined from a

distance-time graph Time is the ___________ variable and

distance is the ______________ variable

Distance-Time Graphs

When speed is constant, a straight line is formed

Why? The slope of any

distance-time graph gives the _______ of the object

An object at rest is a flat line with a slope of _________

Average speed vs. Instantaneous speed

Is describing the motion of an object moving at changing speeds

It is found by dividing distance by time

speed = distance time

r = d t

Describes the speed of an object at any given point in time

Example: a car’s speedometer

Velocity Describes both the speed and the

direction of motion It is found by dividing displacement by

time

v = d velocity = displacement t time

Practice Problem 2 Suppose a lion moves due east at

different speeds so that it travels 25 km in 4.0 hours. What is the lion’s average speed? What is its average velocity?

What would the lion’s average velocity be if it traveled 15 km due north in 2 hours and 15 minutes?

Determining Resultant Velocities

Summary When an object changes position in

comparison to a stationary reference point, the object is in motion.

The average speed of an object is defined as the distance the object travels divided by the time of travel.

The distance-time graph of an object moving at constant speed is a straight line.

The slope of the line is the object’s speed. The velocity of an object consists of both

its speed and its direction of motion.