Define / Describe WORK • Work is done when a force causes an object to move in the direction that the force is applied. • The formula for work is: W = F x d • If there is no movement, there is no work
Units for Work (W=Fd) • Force – newtons • Distance – meters • Work – newton-meter (N-m) or Joule (J)
Two things must happen for work to be done. What are they? • A force must be applied to an object • The object must move in the same direction as the force.
What is Power? • Rate at which work is done • P=W/t or P=Fd/t • Units for Power – joule/sec or watt • Large unit of power – kilowatt (kw) = 1000 watts
What is purpose of a machine? • To make work easier. • Machines do not change the amount of work you do
How do machines make work easier? • They can change the amount of force • They can change the distance (Remember that Work = Force X Distance) • They can also change the direction MORE
How do machines make work easier? Any change in the size of the force changes the distance. No machine can increase both force and distance. • Multiply force – use a smaller effort force over a longer effort distance • Multiply the distance – use a larger effort force over a smaller effort distance • Or, they leave force and distance alone but change the direction in which the load moves.
What is mechanical advantage? The number of times a machine multiplies the effort or input force. • If MA is greater than 1, the effort force is decreased • If MA is less than 1, the effort distance is decreased • If MA = 1, the direction of the effort is changed
Calculating Mechanical Advantage • Ideal MA – does not take friction into account • IMA = de/dr • effort distance divided by resistance distance • MA does not have units • Actual MA – takes friction into account • AMA = Fr/Fe • resistance force divided by effort force
What are the 6 types of simple machines? • There are six simple machines: • The lever, the pulley, and the inclined planeThe wheel and axle, the wedge, and the screw are modifications of these simple machines.
What is a compound (or complex) machine? • A machine made up of two or more simple machines.
Describe LEVER A simple machine made with a rigid bar free to pivot (move) around a fixed point called a fulcrum
Describe the 3 types of levers: • A first class lever is like a teeter-totter or see-saw. One end will lift an object (child) up just as far as the other end is pushed down. • A second class lever is like a wheel barrow. The long handles of a wheel barrow are really the long arms of a lever. • A third class lever is like a fishing pole. When the pole is given a tug, one end stays still but the other end flips in the air catching the fish. MORE
Diagrams of Levers Effort force = input force Load – output force
Diagrams of Levers http://www.professorbeaker.com/lever_fact.html
Describe PULLEYS A simple machine made with a rope, belt or chain wrapped around a grooved wheel. A pulley works two ways.
Diagrams of Pulleys Fixed pulley: http://www.smartown.com/sp2000/machines2000/pulley2.htm Movable Pulley: http://www.smartown.com/sp2000/machines2000/pulley3.htm
How does a pulley work? A pulley works two ways. It can change the direction of a force or it can change the amount of force.
What are the types of pulleys? • Fixed pulley Does not multiply force. Changes the direction of the effort force. Mechanical advantage is equal to one. • Movable pulley Multiplies effort force but cannot change direction of the effort force. Mechanical advantage is the effort distance divided by the resistance distance. • Pulley system A combination of fixed and movable pulleys. Mechanical advantage is equal to the number of supporting ropes.
How does a fixed pulley work? A fixed pulley changes the direction of the applied force. ( Ex. Raising a flag )
How does a moveable pulley work? A movable pulley is attached to the object that is being moved.
What is an inclined plane? A simple machine with no moving parts. It is simply a straight slanted surface. ( Ex. a ramp.)
Diagram of Inclined Plane http://www.smartown.com/sp2000/machines2000/inclinedplane.htm
What is a wheel and axle? A wheel and axle is a modification of a pulley. A wheel is fixed to a axle. The wheel and axle must move together to be a simple machine. Sometimes the wheel has a crank or handle on it. Examples of wheel and axles include roller skates and doorknobs.
Diagram of Wheel & Axle http://www.smartown.com/sp2000/machines2000/wheelandaxle.htm
What is a wedge? A modification of an inclined plane that moves . It is made of two inclined planes put together. Instead of the load being moved up an inclined plane, the inclined plane moves through the load.
Diagram of Wedge The longer and thinner the wedge, the greater the mechanical advantage. www.angelfire.com/scifi/dschlott/ simplemachines.html
What is a screw? A simple machine that is a modified inclined plane. The inclined plane wraps around a shaft and is called threads.
Diagram of Screw The closer together the threads on the screw, the longer the effort distance (or inclined plane). A longer inclined plane increases the mechanical advantage.
Go to this link for more information about machines. Remember to hit the “back” button on your browser to return to this slide show. http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/intro.htm