Chapter 10Motion

10.1: An object in motion changes position

You know that: Objects can move in different ways An object’s position can change

You will learn: How to describe an object’s position How to describe an object’s motion

Position describes the location of an object

Position: The location of a place or object Relative to where you are or your

perspective Relative to another object (reference

point) In order to accurately discuss two

locations: You need to compare the location of the

object with the location of another object or place

Describing a position: Reference point:

A location to which you compare other locations

Longitude and Latitude: Longitude describes how many degrees east

or west a location is from the prime meridian Latitude describes how many degrees north

or south a location is from the equator Graph coordinates:

The x and y coordinates on a graph are reference points.

Measuring distance Standard unit of length:

Meter (m) = 3.3 feet Straight-line distance:

Measurement of the distance between two points when connected by a straight line

Total distance or path distance: The actual distance traveled between

two points Depends on the path you take to get

from point A to point B

Motion is a change in position Motion:

The change in position over time Can be a combination of both

horizontal and vertical position change

Any change in position indicates motion

Described by the object’s speed and direction of travel Faster objects move farther than slower

objects over the same amount of time

Relative motion Motion that is observed from the

observers point of view How an observer sees motion when

compared with his own motion Example:

Page 317: Depending on your point of reference,

either the bus or the street sign is changing position.

relative motion demo

You know: An object’s position is measured from a

reference point You can use distance and direction to

describe the position of an object An object in motion changes position

over time You will learn:

How to calculate an object’s speed How to describe an object’s velocity

Speed: A measure of how fast something moves

or the distance it moves, in a given amount of time.

The rate at which the distance an object moves changes compared to time.

Calculation of speed: You need to know both the distance and

the time Found by dividing the distance the

object travels by the time it takes to cover the distance

Speed = distance ÷ time S = d / t

Standard unit for speed is meters per second (m/s) In the US we measure speed in miles

per hour (mph) One mile per hour = 0.45 m/s

Average speed Instantaneous speed is the “moment

to moment” speed Speed is not constant

When you look at the time it takes a runner to complete 4 laps around the track, you can calculate his average speed Total distance ÷ total time

Distance-Time graphs A graph that plots the distance the

object travels against time. Show you how speed relates to both

distance and time Time is plotted on the x-axis (horizontal) Distance is plotted on the y-axis

(vertical) To determine the speed of an object

from a distance-time graph: Change in distance ÷ change in time

Velocity Velocity:

A speed in a specific direction Vector:

A quantity that has both size and direction Velocity is an example of a vector

Speed is NOT a vector It only measures how FAST or SLOW an

object moves—not the direction Two objects can have the same speed but

different velocities…HOW?

Page 326: Each ant’s direction of motion changes

with the bends in the branch Arrows show the ant’s direction and

speed (longer arrows = faster speed) How do the velocities of each ant

compare?

10.3: Acceleration measures how fast velocity changes

You know that: Speed describes how far an object

travels over a given period of time Velocity is a measure of the speed and

direction of motion You will learn:

How acceleration is related to velocity How to calculate acceleration

Speed and direction change with time

Acceleration: The rate at which velocity changes with

time A measure of how quickly the velocity is

changing If velocity does not change, there is no

acceleration Acceleration is a vector; it has both

size and direction

If acceleration is in the same direction as the object is moving The object is speeding up Positive acceleration

If acceleration is in the opposite direction as the object is moving The object is slowing down Negative acceleration

If acceleration is in at a right angle to the motion The direction of motion will change by some

angle but the speed remains the same

Page 330

Acceleration can be calculated from velocity and time

To measure acceleration, you need to know: The change in velocity by comparing

the initial velocity and the final velocity The time interval used for the change in

velocity The car went from 0 to 60 in 4

seconds Initial velocity Final velocity Time interval

Calculating acceleration final velocity – initial velocity

acceleration = change in time

vfinal - vinitial a =

t Standard unit for acceleration is meters per

second squared or m/s2 because: Velocity is expressed in m/s Time is expressed in seconds

Acceleration can be negative: A car traveling at 10 m/s takes 2

seconds to stop for a red light. What is the acceleration of the car?

vfinal - vinitial a =

t

Velocity-Time graphs pg 334 Shows you a change in acceleration

Time is plotted on the x-axis (horizontal) Velocity is plotted on the y-axis (vertical)

A rising line indicates positive acceleration The steeper the line, the greater the

acceleration A flat line

Indicates no acceleration A falling line

Indicates negative acceleration

graphing acceleration

acceleration comparison