3.6 Turning forces

Recap; Don't forget pressure!

First complete these 10 review questions to reinforce some key ideas from this unit.

Multiple Choice

In science, the standard unit you use to measure speed is;

• kilometers per hour

• meters per hour

• meters per second

• kilometers per second

Multiple Choice

On distance time graph, if the line is ___, the object is moving ___.

If the line is not steep, then the object is moving ___, if the line is ___, then the object is __ ___.

• steep, slowly, fast, flat, at rest

• fast, slowly, steep, at rest, flat

• slowly, steep, fast, flat, at rest

• steep, fast, slowly, flat, at rest

Multiple Choice

What is it called when your speed is changing (increasing or decreasing)?

• Acceleration

• Moving fast

• Moving backwards

• Moving slowly

Multiple Select

What happens when you squash the volume of a gas into a smaller volume? (Select 3 answers)

• There will be more molecules because of a higher pressure

• There will be more collisions between the molecules and the walls of the container

• The pressure increases because there are more collisions

• The temperature increases because there are more collisions

Multiple Choice

The pressure exerted on our bodies by the air around us is known as;

• air pressure

• gas pressure

• pressure

• atmospheric pressure

Multiple Select

Why are liquids incompressible?

(Select two answers)

• The particles in a liquid are touching each other

• There is very little space between the particles

• Liquids are similar to solids

• They have no where to go

Multiple Choice

Arrange the density of spheres, W, X, Y and Z, in descending order.

• X, Y, W, Z

• Y, X, W, Z

• X, W, Y, Z

• W, Z, X, Y

Multiple Choice

Page 166;

How do you calculate pressure?

• Preesure = ForceXArea

• Pressure = Force/Area

• Pressure = Area/Force

• Pressure = Weight

Multiple Select

Which of the following are correct units of pressure? (Select 3 answers)

• N/m²

• N/cm²

• Pascals

• N/m

3.6; Turning forces

Last lesson of this unit! Test next week on Friday.

Lesson objectives;

• Describe what is meant by a moment.

• Calculate the moment of a force.

Use pages 168-169 to complete today's lesson worksheet

Multiple Select

Page 168;

A turning force is;

• A force that turns

• A force that destroys

• A force that acts at a certain distance from the pivot

• A force that pulls

Multiple Select

Page 168;

The 'moment' of a force depends on;

• The force being applied

• How far the force is from the pivot

• The size of the pivot

• the length of the pivot

Multiple Choice

Page 168;

When an object is in equilibrium, the sum of clockwise moments = the sum of anti-clockwise moments.

This statement is ..............

• The law of inertia

• The law of gravity

• The law of momentum

• The law of moments

Multiple Choice

The law of moments states that "When an object is in equilibrium ..............."

• Forces on a seesaw must balance

• Clockwise forces = Anticlockwise forces

• Clockwise moments = Anticlockwise moments

• Forces on a seesaw have to be on opposite sides

Multiple Select

The law of moments states that "When an object is in equilibrium, the sum of clockwise moments equals the sum of anti-clockwise moments"

This means;

• The moments cancel out

• The net / sum of clockwise and anti-clockwise moments is 0

• The clockwise and anti-clockwise forces are equal

• All of these

Calculating moments

To calculate the turning effect / moment of a force, we use the formula

Moment = Force X Perpendicular distance from the pivot

Multiple Choice

What is the equation for moments?

• Moment = force x perpendicular distance from pivot

• Moment = mass x velocity

• Moment = force x distance

• Moment = force x parallel distance from pivot

Multiple Choice

Moment can be calculated using the equation:

• M = F × d

• M = F / d

• M = F² × d

• M = F / d²

Multiple Choice

What is the moment acting on the seesaw?

• 1.6Nm

• 15Nm

• 16N

• 4Nm

Activity

Go to the link; https://phet.colorado.edu/sims/html/balancing-act/latest/balancing-act_en.html

Play around with the simulation and use it to answer the following questions.

Multiple Choice

What is the sum of the clockwise and anti clockwise moments in this picture?

• Clockwise = 120, anticlockwise = 120

• Clockwise = 60, anticlockwise = 120

• Clockwise = 120, anticlockwise = 30

• Clockwise = 30, anticlockwise = 120

Multiple Choice

What is the sum of the clockwise and anti clockwise moments in this picture?

• Clockwise = 400, anticlockwise = 420

• Clockwise = 420, anticlockwise = 400

• Clockwise = 80, anticlockwise = 60

• Clockwise = 60, anticlockwise = 80

Multiple Choice

The boys in this picture have the same mass.

Which of the following is true about the force they exert, and the moments created by their forces?

• Same force and same moments

• Same force but different moments

• Different forces and different moments

• Different forces, same moments

Multiple Choice

Use the simulation link

Where can Elisha place a 10Kg mass to set the systems in equilibrium?

• Position 4, right of the pivot

• Position 2, left of the pivot

• Position 2, right of the pivot

• Position 4, left of the pivot

• Position 5, left of the pivot

Multiple Choice

Use the simulation link;

Where should this dad sit to balance his son?

• 0.25 metre mark, right of the pivot

• 0.25 metre mark, left of the pivot

• 0.5 metre mark, right of the pivot

• 0.5 metre mark, left of the pivot

Multiple Choice

Use the simulation link

What is the mass of this mystery object?

• 10 Kg

• 20 Kg

• 40 Kg

• 8 Kg

Multiple Choice

Can you figure out the mass of the mystery object?

• 30 Kg

• 15 Kg

• 25 Kg

• 20 Kg

Multiple Choice

What is the moment produced by the 15 N?

• 15 Nm (clockwise)

• 150 Nm (anti - clockwise)

• 1.5 Nm (anti - clockwise)

• 0.15 Nm (clockwise)

Fill in the Blanks

Multiple Choice

A third weight is to be added to bring the system into equilibrium. What is its magnitude and where should it be placed?

• 1N, 2 m to the left of the pivot

• 1N, 3 m to the right of the pivot

• 2N, 1 m to the left of the pivot

• 2N, 1 m to the right of the pivot

Multiple Select

Page 169; All the weight of an object acts through a point known as the ______________ (Select two answers)

• centre

• centre of mass

• centre of gravity

• centre of motion

Multiple Choice

Page 169;

If the centre of gravity is above the pivot .................

• there is no moment

• there is a clockwise moment

• there is an anticlockwise moment

Multiple Choice

Page 169;

If the centre of gravity is to the left of the pivot .................

• there is no moment

• there is a clockwise moment

• there is an anticlockwise moment

Multiple Choice

Page 169;

If the centre of gravity is to the right of the pivot .................

• there is no moment

• there is a clockwise moment

• there is an anticlockwise moment

Multiple Choice

Google this;

Where is the world's largest seesaw?

• New York

• Illinois

• Chicago

• Springfield

Multiple Choice

If you need to balance a 200kg mass placed 2meters near the pivot of the seesaw, Should you sit on the same side or the opposite side of the pivot as the mass?

• Same side

• Opposite side

• Doesn't matter, you can't balance it

Multiple Choice

If you need to balance a 200kg mass placed 2meters near the pivot of the seesaw, Should you closer than 2m from the pivot or further than 2m from the pivot?

• Closer

• Further

• Doesn't matter, you can't balance it

HW & Extra Credit

HW; Complete level 1 of the game tab on the simulation link. (Submit screenshots on google classroom)

https://phet.colorado.edu/sims/html/balancing-act/latest/balancing-act_en.html

Extra credit; Each extra level = 10 points! (submit screenshots)