Chapter 3 SPEED

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 hrs Distance = 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 speed Time = 110km 95km/h Time = 1.15h

Distance-Time Graphs When 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 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 = m/s² 7 s 7 s

Velocity-Time Graphs This 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.