Chapter 3 SPEED. Distance = Speed X Time Answer can be in metres (m) or kilometres (km)

Chapter 3SPEED

Distance = Speed X Time

Answer can be in metres (m) or kilometres (km)

A car drove at 72km/h for 3 hours. Calculate the distance travelled.

Distance = 72 km X 3 hrsDistance = 216km

Speed = Distance Time

Answer can be in metres per second(m/s) or kilometres per hour

(km/h)

A girl ran 12km in 1hr and 30mins. Calculate her average speed.

• Speed = Distance Time• Speed = 12km 1.5hrs•Answer = 8km/h

Time = Distance Speed

Time can be measured in seconds (s) or hours (h)

John drives to Dublin a distance of 110km. His average speed for his journey is 95km/hr.

How long did it take John to get to Dublin?

Time = Distance speedTime = 110km 95km/hTime = 1.15h

Distance-Time GraphsWhen we calculate the speed throughout a

journey we get an average.

If we want a speed for a more specific point in time we could use a distance time graph.

These graphs are simple and easy to use.

Velocity

The velocity of an object is its speed in a certain direction

Question

• You are about to run a 100metre race.• Someone tells you the wind-speed is

40km/h.

• Would you be happy or sad?• What difference could the wind speed

make to the time it takes you to run 100m?

• So its not just the speed that’s important. The direction is also crucial.

Velocity

• A car has an accelerator. If you put your foot on the accelerator you can increase the speed or velocity of the car in a certain direction• Acceleration is the difference in

speed now and the speed one second from now.

Acceleration

Acceleration• Acceleration is the rate of change of

velocity (or speed)

Acceleration = Change in Velocity or speed Time Taken

Measured in m/s²

Q. In a race a car changed its velocity from 0m/s to 102m/s in 7 seconds. What was its acceleration?

A. (Final Velocity – Initial Velocity)

Time taken

= (102 – 0) m/s = 102 m/s = 14.57 m/s² 7 s 7 s

Velocity-Time GraphsThis graph allows us to measure the change in

velocity over a certain time period.

It also allows us to measure acceleration.

These graphs are simple and easy to use.

Chapter 3

Area, Volume and Density

AREA• The area of shape is the size

of its surface

The area of a triangle is the space enclosed by the three lines

Area of a rectangle= length x width

•Area is measured in metres squared (m²) or centimetres squared (cm²)

Area = 8 x 5 cm = 40cm²

Area = 5 x 6 cm = 30cm²

Area of triangle = ½ the base x perpendicular height

3cm x 4.5cm = 13.5cm²

Area of a circle = Radius (r) x radius (r) x π (3.14)

Area of a circle = 4cm x 4cm x 3.14 = 50.2cm²

4cm

VOLUME The volume of an object is the

amount of space is it takes up

Volume is measured in cubic metres (m³) or cubic centimetres (cm³)

•Volume is also measured in litres (l) •1 litre = 1000cm³

Volume of a Solid• If its a regular shape then we use the formula:

Length x width x height

8CM X 5CM X 3CM = 120CM³

Volume of a Solid• If its an irregular shape then we use displacement

Remember always take your reading from the bottom of the meniscus.

Mass•Which is heavier a tonne of

feathers or a tonne of coal?• There the same

•Which is heavier, lead or water? •At first it seems logical that

lead is heavier than water•Buts its not a fair question...• To make it fair we need to

compare the mass of a similar volume of each.

Mass• The mass of an object is the

quantity of stuff or ‘’matter’’ in it. •Mass of 1cm³ of water = 1g•Mass of 1cm³ of lead = 11.2g

• In science we call the ‘mass per unit volume’ of an object its density.