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.
