Do now!

1
Do now!
Can you write the following words five times in
the back of your books. Resistance, magnetism,
upthrust
2
Todays lesson

• What is a force?
• Contact and non-contact forces
• Units of force
• Measuring forces

3
What is a force?

• A force is a push (or a pull)

4
What is a force?

• A force can change the shape of an object

5
What is a force?

• A force may also change the speed and direction
  of an object

6
Contact forces

• Many forces need contact to affect an object

7
Non-contact forces

• Some forces can affect an object from a distance

8
Measuring force

• We can measure a force with a forcemeter

Forces are measured in units called NEWTONS.
9
Measuring forces
The force of gravity pulling on an apple is about
1 N
1 N
10
Measuring forces
The force needed to pull a truck is about 3000 N
3000 N
11
Lets measure some forces!
Can you stick the sheet in?
12
Todays lesson

• Upthrust
• Measuring upthrust
• Floating and sinking

13
Upthrust

• Gently lower a mass on a Newton meter into a
  beaker of water. Sketch a diagram in your book
  and write a sentence describing what happens.

14
What happens if the upthrust is equal to the
force of gravity?
15
What happens if the upthrust is equal to the
force of gravity?
16
Which is heavier?
5 kg
5 kg
17
Density
5 kg
5 kg
18
Density

• Density is the mass of one cubic centimetre of
  a substance.
• So for example, gold has a density of 19.3
  g/cm3. This means one cubic centimetre (cm3) of
  gold has a mass of 19.3 grams.

19
The formula!
g/cm3
g

• Density mass
• volume
• Or using the formula triangle
• m
• D x V

cm3
20
Density of regular shapes

• volume length x width x height
• density mass/volume
• mass using a scale

height
width
length
21
Now lets measure some densities.