a) Calculate the total anticlockwise *moments

b) Calculate the total clockwise moments

c) Is this system in equilibrium?

*moment = another name for torque

4 kg 2 kg

20 cm35 cm 20 cm

2 kg

Starter

A car is moving at a steady velocity of 20 ms-1. The mass of the car and its passengers is 1200 kg.1. If the thrust force is 4000 N, find the

friction force.

2. Draw a free body diagram with labels AND sizes of all forces

3. What would happen to the car’s motion if the thrust force was suddenly removed?

1 Peter Jacob T Frankie

2 Liam David Scott

3 Will R Tim Jakob O

4 Will K Callum Best

5 Hayden Sam Rodrigo

6 Tom Will S (Cameron)

Free Body Diagrams

Finish by Tomorrow (Friday)

1. Homework Booklet Sheet #5 Q 1 ~ 9 (except for Q5)

2. Purple Worksheets pg. 52 ~ 54

3. Extension work (optional): Activity 9A textbook pg. 109

Tutorials – 2 hours (expected)

Franky – Friday after schoolWill K – Friday after schoolJakob – Friday after schoolJacob – Friday after schoolWill S – Friday after schoolTim – Friday after schoolDavid – Friday lunch time (50 min)Sam – Sunday 10amScott – Sunday 10am

What is Torque?• Turning effect about a pivot

• Force that tries to ‘rotate’ an object

• ‘Spinning force’

• τ = torque (a.k.a. moment)• F = force• d = distance from the pivot• Torque is measured in ______• Clockwise or Anticlockwise

Pivot

Pivot = the stationary point about which the torque can act or an object can revolve

The relationship between F and d

Question A force of 10 N which acts at 8 cm from the pivot is needed to lift the cap off a bottle of soft drink as shown below.Find the size and the direction of the torque being applied.

What is Equilibrium?

Fnet = 0

τnet = 0

τnet = 0

Total Total Clockwise + Anticlockwise = Moments Moments

0

It means…

a) Calculate the anticlockwise torque

b) Calculate the clockwise torque

c) Which is greater? Anticlockwise torque or clockwise torque?

12 kg 8 kg

60 cm40 cm

Example #1

a) Calculate the anticlockwise torque

b) Calculate the clockwise torque

c) Which is greater? Anticlockwise torque or clockwise torque?

7 kg 13 kg

35 cm65 cm

Example #2

a) Calculate the total anticlockwise *moments

b) Calculate the total clockwise moments

c) Is this system in equilibrium?

*moment = another name for torque

9 kg 4 kg

30 cm40 cm 30 cm

4 kg

Example #3

Aaron (70 kg) Bob (50 kg)

Aaron is 1.5 m away from the pivot whereas Bob is 2 m away from the pivot. What will happen to the see saw?

Where do you think Bob will have to be to balance the see saw?

The mass of the rock is 100 kg and it is sitting on one end of the stick, 50 cm away from the pivot as shown in the diagram.

If the man exerts a force of 200 N downwards to the other end of the stick which is 3 m away from the pivot, would he be able to lift the rock?

"Give me a place to stand and I will move the earth!"

Archimedes

Is this system at equilibrium?

700 g300 g

70 cm30 cm

Centre of Mass• The weight of an object acts down

through the object’s centre of mass.

• This is the point at which, if an object is suspended or pivoted, the object will balance.

• Watch out for any objects of “negligible mass”

700 g300 g

70 cm30 cm

700 g300 g

Fw (weight of the ruler)

Fs (support force)

7 N3 N

Fnet = 07 + 3 + Fw + Fs = 0

Torque Exercises

• Activity 9B (pg. 116) Q5, 6, 7 only

• Homework Booklet Worksheet #12 first page only

• Extension Work: Homework Booklet Worksheet #12 second page AND Activity 9B Q8, 9, 10, 11 and 12