Work and Simple Machines

1. Work and Simple Machines

2. What is a machine? • A machine is a device that uses energy to perform some activity. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work. A simple machine is a device that transforms the direction or magnitude of a force.

3. How do we know when work has been done on an object? Mrs. Jern ! Get your foot off the brake !!! • When a force acts upon an object to cause a displacement of the object, it is said that work was done upon the object. Three key ingredientsto work - force, displacement, and cause. In order for a force to qualify as having done work on an object, there must be a displacement and the force must cause the displacement.

4. Work • The equation for work is: W = F x d • The units of work are Joules,J. (1 N●m = 1J) • The units of force are Newtons, N. • The units of distance is Meters, m. A force is applied to an object. It is moved a distance of 1 m. If we apply twice the force to move the object 1 m, how much work did we do on the object?

5. Answer the following… • A force of 120 N is used to lift a 10 kg box to a height of 5.0 m. How much work is done on the box? • A child pulls a sled up a snow-covered hill. The child does 450 J of work on the sled. If the child walks 15 m up the hill, how large of a force must the child exert? • You must exert a force of 6.0 N on a box to slide it across a table. If you do 3.0 J of work in the process, how far have you moved the box? • How much work is done on a small car if a 3200 N force is exerted to move it 80.0 m to the side of the road?

6. Work done on a textbook No work is done on a textbook when it is held at rest. No work is done on a textbook when it is carriedhorizontally at a constant velocity. Positive work is done on a textbook when it is raised vertically at a constant velocity. Negative work is done on a textbook when it is lowered diagonally at a constant velocity. Positive work is also done on a textbook when it is raised diagonally at a constant velocity. Negative work is also done on a textbook when it is lowered vertically at a constant velocity.

7. Work • W = Fd - remember the d must be in the same direction as the force. The force must cause motion in the direction of the force for work to be done. • Ex: If a student pushes a wall with all of his strength - he has done no work on the wall (if the wall does not move) • Also a student carrying a book does NO work on the book because the force and motion are NOT in the same direction.

8. Work done on a textbook No work is done on a textbook when it is held at rest. No work is done on a textbook when it is carriedhorizontally at a constant velocity. Positive work is done on a textbook when it is raised vertically at a constant velocity. Negative work is done on a textbook when it is lowered diagonally at a constant velocity. Positive work is also done on a textbook when it is raised diagonally at a constant velocity. Negative work is also done on a textbook when it is lowered vertically at a constant velocity.

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

12. Wheels and Axles • The wheel and axle are a simple machine • The axle is a rod that goes through the wheel which allows the wheel to turn • Gears are a form of wheels and axles

13. Pulleys • Pulley 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

14. Inclined Planes • An inclined plane is a flat surface that is higher on one end • Inclined planes make the work of moving things easier

15. Wedges • Two inclined planes joined back to back. • Wedges are used to split things.

16. Screws • A screw is an inclined plane wrapped around a shaft or cylinder. • The inclined plane allows the screw to move itself when rotated.

17. Levers-First Class • In a first class lever the fulcrum is in the middle and the load and effort is on either side • Think of a see-saw

18. Examples of 1st Class Levers • Seesaw (also known as a teeter-totter) • Crowbar • Pliers (double lever) • Scissors (double lever)

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

20. Examples of 2ndClass Levers • Wheelbarrow • Nutcracker (double • lever) • The handle of a pair • of nail clippers • An oar

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

22. Examples of 3rd Class Levers • Human arm • Tongs (double lever) (where • hinged at one end, the style • with a central pivot is first- • class) • Catapult • Any number of tools, such • as a hoe or scythe • The main body of a pair of • nail clippers, in which the • handle exerts the incoming • force.

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

24. Mechanical Advantage • Basic Formula: IMA = E / R • IMA = Ideal Mechanical Advantage E = effortR = Resistance Effort will usually be a distance: cm, m IMA is a multiplier.  Meaning it represents how much the machine will multiply the force which is put into it.  It, therefore, has no unit and would be written like:  3.  This means that whatever amount of work is put into the machine, you will get 3 times the work out.

25. IMA of a Lever Length of effort arm Length of resistance arm IMA =

26. IMA of a Wheel and Axle Radius of Wheel Radius of Axle IMA =

27. IMA of an Incline Plane Length of slope Height of slope IMA =

28. IMA of a Pulley Notice the number of ropes sharing the load !