Lesson Objectives

At the end of this lesson, students will be able

to:

1.Explain the relationship between• Distance,• Speed and• Time

2.Use spreadsheets to show relationships and present information clearly and/or succinctly

3. Draw appropriate type of graph, using

excel, to convey information

Motion

Motion is movement.

Many objects around us can move and if the speed ofthese Objects can be determined, then their motion canbe measured.

DistanceDistance is how far it is between two points and is

measured in metres (m), kilometres (km) Or millimetres (mm).

• The choice of unit would depend on how far is theDistance to be or measured.

• Other multiple units often used in distance measurement include mirometres (μM) and nanometres (ηM)

Time

Time is a measure of how long it takes between two events.

• It is often measured in seconds (s), minutes (min), hours (h), days and weeks.

SpeedSpeed is defined as how fast an object is moving or the distance travelled in a given time• Speed is measured in metres per second (m/s) or in the case of a car, in kilometres per hour (km/h)

Velocity is speed in a given direction. The measurement of velocity is important for ships at sea, aircraft and inter-planetary space probes as it tells the speed and direction of motion.

• When travelling in a car, the speed changes during the journey. This may be due to slowing down at a roundabout, a stop at a traffic light or travelling from a Suburban road to the freeway etc.

• The speedometer of a car gives the speed of the car at the instant of looking at it – this is the instantaneous speed.• The Police use radar guns to measure the instantaneous speed of cars in motion on the road.

Average Speed is the speed at which a car would travel if it went at the same speed throughout a journey.

The relationship between distance, speed and time can be expressed as follows:

Average speed = distance travelled/time taken

The relationship between Distance, Speed and Time

Calculating Speed, Distance and Time

For example:1. If a car travels 120km in 2 h, its

Average speed = 120km/2h = 60km/h

Or,2. If Joan drives at an average speed of 45km/ on a journey of 135km, the journey would take:

Time = 135km/45km/h = 3 hours.Or

3. Chris cycles at an average speed of 8km/h 3 hours. He travels a

Distance of 8km/h x 3h = 24km.

DISTANCE-TIME GRAPHS Distance-time graphs can be used to describe journeys. This type of graph is plotted with distance on the vertical (y) axis and time on the horizontal (x) axis.

The graph below describes 3 parts of a journey:

In the above graph, the gradient of the straight line is a measure of the speed of the moving object

Note: negative gradient would indicate that the object is moving towards the starting point.

EXAMPLES1. The following graph describes the journey of a snail.

a. Describe the motion of the snail.b. What is the speed of the snail during each part of the journey?

Solution:a. The first part of the graph showed that the snail travelled away from

the start point for 1000 m in 80 s, at a constant speed.

The second part (horizontal) shows that the snail stopped for 20 s.

The third part shows the snail returning to the start point at a constant speed and taking 100 s to do so.

b. During the first stage, the snail travelled with a:

Speed = 1000m/80 s = 12.5 m/s.

During the second stage, the speed of the snail was 0 as it was at rest.

And finally, the snail returned to the starting point at a

Speed of 1000 m/100 s = 10 m/s.

Speed-Time Graph

Speed-Time graphs are used to describe the distance travelled by an object.

They are plotted much the same like Distance-Time graphs. Time as the

independent variable is plotted on the x-axis while speed is plotted on the y-axis.

Speed-Time graphs are also called Velocity-Time graphs.

This graph, with a straight horizontal line shows constant speed

The graph shows that the speed of the object is increasing or the object is accelerating.

This graph shows that the speed of the object is decreasing or the object is decelerating.

In summary:

http://youtu.be/AcByglYNCqw

Please watch the YouTube video below to refresh your memory on how to use excel to plot Distance-Time Graphs.

Note that the data set used in the video will be different from the one in your topic test but the concept for plotting the graph is the same.

In preparation for your class task:

Please logon to your group page on edmodo and complete the task in your.

This assignment will count for 10% towards your term 2 assessment and is due .