Work and Simple Machines

SWBAT define work; distinguish the different types of simple machines; explain how machines make work easier

Work

• Work• is done when a force causes and object to move in the same

direction as the force that is applied.• What is work measured in?

• Joules, named after James Prescott Joule, who showed that work and energy are related

• Work Equation• Work = Force x Distance• W = Fd

Applying Math

• A weight lifter lifts a 500 N weight a distance of 2 meters from the floor to a position over his head. How much work did he do?

• In your groups try the following two problems:• Using a force of 50 N, you push a computer cart 10

meters across the classroom floor. How much work did you do?

• How much work does an Olympic sprinter do while running a 200 meter race with a force of 6 N?

What is a machine?

• Simple machine • a machine that uses only one movement.

• Compound machine • a combination of simple machines.

• How do machines make work easier?• Can change the size of force you apply• Can change the direction of the force

Mechanical Advantage

• Mechanical advantage • the number of times the applied force is increased by

a machine.• Mechanical advantage equation

• Mechanical advantage = force out force in

MA = Fo_ Fi

Simple Machines

• Pulley • is an object, like a wheel, that has a groove with a

rope or cable running through it.• Lever

• is a rod or a plank that pivots about a fixed point. The pivot point is called the fulcrum.

3 classes of levers

• First Class Lever• The fulcrum is between the input and output force.

Fulcrum

Load

Effort

3 classes of levers

• Second Class Levers• The output force is applied between the input force

and the fulcrumLoad

Effort

Fulcrum

3 classes of levers

• Third Class Levers• The output force is applied at the bottom end of the

stick.Load

EffortFulcrum

Simple Machines

• Wheel and axle • is made of two round objects that are attached and

rotate together about the same axis.• Inclined plane

• a sloped surface, sometimes called a ramp.

Simple Machines

• Wedge • a moving inclined plane, with one or two sloping

sides. It changes the direction of the input force.• Screw

• an inclined plane that wraps around a post.