Bell Question 1/23/12 What force makes machines less efficient? What is the equation for measuring efficiency? What is the efficiency of a machine that has an output of 600 J when 800 J of work are put into the machine?

Inclined Plane A flat sloped surface

How it works: exert a force over a longer distance Mechanical advantage : divide the length of the incline by its height.

Wedge A device thick at one end and tapers to a thin edge at the other end.

How it works: move inclined plane turns the output force at 90° angle Mechanical advantage : length of the wedge divided by the width.

Screw An inclined plane wrapped around a cylinder

How it works: threads increase the distance over which you exert the input force, output force pulls the screw into the object. Mechanical advantage: the closer the threads the greater the M.A. , Length around the threads divided by the length of the screw.

Bell Questions 1/25/12 A _____________ is a device that is thick at one end and tapers to a thin point at the other end. A __________ is an inclined plane wrapped around a cylinder. What is the ideal mechanical advantage of this inclined plane? 8 m 2 m

LEVER Lever – a rigid bar that is free to pivot, or rotate on a fixed point (fulcrum) Mechanical advantage = distance to input distance to output

1st Class Lever – Change the direction of input force 1st Class Lever – Change the direction of input force. The fulcrum is between the output force and input force.

2nd Class Lever – increase the force, they don’t change the direction of the force. (output force in the middle)

3rd Class Lever – increase distance, don’t change direction 3rd Class Lever – increase distance, don’t change direction. (input force in the middle)

Bell Questions 1/30/12 You exert a force of 25 newtons to push a box 10 meters. How much work did you do on the box? An ideal machine would have an efficiency of _______%. If scissors have an efficiency of 60%, 40% of your work is lost due to what force?

Wheel and Axle two cylindrical objects fastened together and rotate on a common axis Large radius is the wheel, small radius is the axle.

How it works – increases force, must exert force over a longer distance Mechanical advantage = Radius of wheel Radius of axle

Pulley grooved wheel with a rope or cable.

How it works – increases the effect of your input force and changes direction of input force. Mechanical advantage - number of sections of rope that support the object.

Fixed pulley – does not change the amount of force applied, only changes direction Moveable pulley – increase amount of force applied, does not change direction Block and tackle – both fixed and moveable pulleys

Bell Questions 1/31/12 Name the six kinds of simple machines (see if you can do it without looking in your notes or your book)

Compound Machine – a device that combines two or more simple machines. Examples Wheel barrow Scissors bicycle