What is work?

In science, the word work has a different meaning than you may be familiar with.

The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

Work or Not?

According to the scientific definition, what is work and what is not? a teacher lecturing

to her class a mouse pushing a

piece of cheese with its nose across the floor

What’s work?A scientist delivers a speech to an

audience of his peers. A body builder lifts 350 pounds

above his head. A mother carries her baby from room

to room. A father pushes a baby in a carriage.A woman carries a 20 kg grocery bag

to her car?

What’s work?What’s work?A scientist delivers a speech to an

audience of his peers. NoNoA body builder lifts 350 pounds

above his head. YesYesA mother carries her baby from room

to room. NoNo A father pushes a baby in a carriage. YesYesA woman carries a 20 km grocery

bag to her car? NoNo

Formula for work

Work = Force x Distance

The unit of force is newtonsThe unit of distance is metersThe unit of work is newton-metersOne newton-meter is equal to one jouleSo, the unit of work is a joule

History of Work

Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.

Simple Machines

Helping us lift, lower, fasten, split, cut, divide, and move!

Simple Machines

Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

What is a Simple Machine?A simple machine

has few or no moving parts.

Simple machines make work easier

Simple MachinesThere are 6 simple machines

Wheel and AxlesPulleys Inclined PlanesWedgesScrewsLevers

Wheels and Axles A wheel and axle is a lever

that rotates in a circle around a center point or fulcrum.

The axle is a rod that goes through the wheel which allows the wheel to turn

Makes it easy to move things by lifting or rolling them, and reducing friction

Examples: car, bicycle, office chair, wheel barrow,

shopping cart, door handlehand truck, roller skates

Wheels and AxlesGears are a form of a wheel and axleA gear is a wheel with teeth. The teeth fit in between each other and

turn. When one gear turns, its teeth push

against the teeth of the other gear and they both turn.

There are gears on your bike, on a can opener and on an egg beater.

Pulleys Pulleys are wheels and

axles with a groove around the outside

A pulley needs a rope, chain or belt around the groove to make it do work

Makes lifting heavy weights easier by redirecting force

Pulleys let you move loads up, down, or sideways.

Types of Pulleys A fixed pulley is a pulley in

which the wheel does not move A moveable pulley does not change the direction of

the effort force but does increase the size of the force. When you pull on the rope, the pulley and the load come up.

A compound pulley, also called a block and tackle, is a combination of a fixed and a movable pulley. This type of pulley changes direction, and yields a gain in force at the same time.

Inclined Planes An inclined plane is a flat

surface that is higher on one end

Inclined planes make the work of moving things easier

Makes it easier to move objects upward; a longer path, but easier lifting

Wedges Two inclined planes

joined back to back. Wedges are used to

split things. Pushes material apart, cuts

Screws A screw is an inclined

plane wrapped around a shaft or cylinder.

The inclined plane allows the screw to move itself when rotated.

Turns rotation into lengthwise movement

Screws are inclined planes wrapped around a cylinder. They also act like a wedge albeit with just one edge to separate things. The more gentle the curving, the less force needed but it is needed over a longer distance. If you have tighter curving, you need more force and move less distance as the screw turns.

Levers-First Class In a first class lever the

fulcrum is in the middle and the load and effort is on either side

Helps lift heavy weights using longer distances

a car jack, a pair of pliers, a pair of scissors, a water pump, a balance or pair of weigh scales, a crowbar

Levers-Second Class In a second class

lever the fulcrum is at the end, with the load in the middle

Think of a wheelbarrow

Levers-Third Class In a third class lever

the fulcrum is again at the end, but the effort is in the middle

Think of a pair of tweezers or a baseball bat

SUMMARYWedge Pushes material apart, cuts

Wheeland Axle

Makes it easy to move things by rolling them, and reducing friction

Lever Helps lift heavy weights using longer distances

Inclined Plane

Helps lift heavy weights using longer distances

Screw Turns rotation into lengthwise movement

Pulley Makes lifting heavy weights easier by redirecting force

Pulleys let you move loads up, down, or sideways.

Simple Machines Simple Machines

can be put together in different ways to make complex machinery

Simple Machine

Diagram Describe how it worksAn unique example