What is work?

1. 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.)

2. 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

4. 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?

5. What’s work? • A scientist delivers a speech to an audience of his peers. No • A body builder lifts 350 pounds above his head. Yes • A mother carries her baby from room to room. No • A father pushes a baby in a carriage. Yes • A woman carries a 20 km grocery bag to her car? No

6. Formula for work Work = Force x Distance • The unit of force is newtons • The unit of distance is meters • The unit of work is newton-meters • One newton-meter is equal to one joule • So, the unit of work is a joule

7. 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.

8. Simple Machines Helping us lift, lower, fasten, split, cut, divide, and move!

9. 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.

10. What is a Simple Machine? • A simple machine has few or no moving parts. • Simple machines make work easier

11. Simple MachinesThere are 6 simple machines • Wheel and Axles • Pulleys • Inclined Planes • Wedges • Screws • Levers

12. Wheels and Axles • A wheelandaxle 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

13. Wheels and Axles • Gears are a form of a wheel and axle • A 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.

14. 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 moveloadsup, down, or sideways.

15. 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.

16. 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

17. Wedges • Two inclined planes joined back to back. • Wedges are used to split things. • Pushes material apart, cuts

18. 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. 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

19. 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

20. Levers-Second Class • In a second class lever the fulcrum is at the end, with the load in the middle • Think of a wheelbarrow

21. 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

22. SUMMARY

23. Simple Machines • Simple Machines can be put together in different ways to make complex machinery