Unit 305 session 10 principles of simple machines

​​The principles behind simple machines 

Open Ended

What do you think a machine is?

​The principles behind simple machines 

​Levers 

A lever is an object that is used with a pivot point, or 'fulcrum', to multiply the force applied to another object. 

​Levers use the principle of mechanical advantage. 

Mechanical advantage = load ÷ effort 

Multiple Choice

1. Using a lever, Joe is able to lift a 10,000 N car off of the ground with a force of 

 1000 N. What is the mechanical advantage of the lever? 

• 1

• 10

• 100

• 1000

​Wheels and axles 

​There are two basic ways a wheel and axle can work together to help move things. 

1. The Force is applied to the Wheel

For example, a screwdriver is an example of a wheel and axle.

The handle is the wheel where the force is applied. It turns or spins and increases the force of the shaft or axle, which helps turn the screw. 

​Another example of force being applied to the wheel is when a doorknob is turned.
The wheel (doorknob) is turned and the locking mechanism connected to the shaft turns and the door can then be opened. 

​2. The Force is applied to the Axle 

A Ferris wheel is an example of force being applied to the axle.

When the axle turns it results in the giant wheel turning.

The wheel is much larger than the axle and covers more distance and area.  

Multiple Choice

What is the mechanical advantage of a wheel and axle system where the radius of the wheel is 10 cm, and the radius of the axle is 2 cm?

• 2

• 5

• 10

• 20

​Gears

​Gears, like those shown, are special wheels with teeth called threads located on the outside of the wheel. Gears also need axles. The gears can be found in different sizes and are arranged with their teeth interlocking. Gears can be found on bicycles, which also uses a force applied to the axle to help its wheels move. 

​Pulleys 

​A pulley is simply a wheel with a groove in it, and a rope in the groove. It is also called a drum or a sheave.
The groove is important because it helps to keep the rope in place. It is used to lift up or lower heavy objects.
With a pulley, an object to be lifted can be tied to one end of the rope, and a force is applied to the other end by pulling the rope downwards.
The downward force turns the wheel with the rope and pulls the load upwards at the other end.  

​How pulleys work 

The more wheels you have, and the more times you loop the rope around them, the more you can lift. 

​Mechanical advantage = Load
Number of pulleys

Multiple Choice

What is the mechanical advantage of a system with two pulleys

• 2

• 4

• 6

• 8

​Screws 

​A screw is a simple machine that works as a modified inclined plane.  

The mechanical advantage of a screw is the circumference of the shaft divided by the thread pitch. 

Multiple Choice

What type of motion does a screw convert into linear motion?

• Oscillatory

• Translational

• Rotational

• Vibrational

​Equilibrium  

​The condition of a system in which all competing influences are balanced. 

Multiple Choice

What is the primary mechanical advantage of using the simple machine seen in the image? 

• You can apply a large force and have it penetrate over a very long distance.

• You can apply a long distance and have it convert into a very short distance. 

• You can apply a short distance and have it multiplied to penetrate a large distance. 

• You can apply a small force to penetrate something that normally requires a large force. 

Multiple Choice

If you use a crowbar to get the lid off of a bucket, what simple machine are you using?

• Inclined Plane 

• Lever 

• Pulley 

• Wheel and Axle 

Multiple Choice

What is the mechanical advantage of this pulley system?

• 2

• 3

• 4

• 5

Multiple Choice

5. This 2000 N weight is raised 1 meter by pulling 4 meters of rope. 

 What force was required to pull the rope?

• 500N

• 1000N

• 2000N

• 8000N

Multiple Choice

What is mechanical advantage? 

• The advantage a machine has over a bicycle 

• A measure of how much a simple machine reduces work

• A measure of when is the best time to use a simple machine 

• A measure of the force amplification achieved by using a tool