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# Simple Machines

What is a pully and how does it work? It uses a grooved wheel or wheels and a rope. A pully system can be set up to change direction of a force, or multiply a force.
What is a lever, and how does it work? It uses a stiff bar supported by a point called a fulcrum. When a force is applied to one end, the lever pivots on the fulcrum, and the opposite end of the lever moves in the opposite direction. It may multiply force depending on placement of the fulcrum.
What is a wedge, and how does it work? It is a device that is wide at one end, and tapers smaller towards the other end. It changes the direction of the force.
What is a wheel and axle, and how does it work? It is a round object (called a wheel), with a rod through the center (called an axle), and the wheel spins on the rod.
What is an inclined plane, and how does it work? It is a flat, sloped surface that allows a person to exert the force over a longer distance.
What is a screw, and how does it work? A screw is an inclined plane wrapped around a cylinder. As the screw is turned, the threads drive the screw into the piece of wood or other object.
What is the difference between work and power? Work is force applied with the object moving a distance in the same direction as the force. Power is the rate that work is done
Is it possible to do work without applying power? Defend your answer Yes, without a time value work can still be calculated.
Sally lifts a book and carries it to the table. When is she working? How do you know? She is working when she lifts the book (applied force and movement in the direction of the force). She is not working when she is carrying the book to the table (force is up and movement is horizontal).
What is the formula for work? Work= force x distance
What are the units for work? Joules or N*m
How much work is done by a crane that lowers 1,000 Newtons of material a distance of 150 meters? W= (1000N)(150 m) =150000 J
You use 35 J of energy to move a 7.0 N object. How far did you move it? Distance = (35 J)/(7 N) =5 m
What is the formula for Power? Power =Work/Time
What are the units for power J/s or Watts
A 49 newton rock is lifted 2 meters in 5 seconds. How much work is done? What power is used? Work = (49 N)(2m) =98 J Power= (98J)/(5 s)=19.6 W
A student who weighs 500 Newtons climbed the stairs from the first floor to the third floor, 15 meters above, in 20 seconds. How much work did she do? What was her power? Work = (500N)(15m)=7500J Power= (7500J)/(20s) =375 W
What do machines do? What are the three ways they do so? Make work easier. They can change the force, distance, or direction
Machine one has a mechanical advantage of 4. Machine two has a mechanical advantage of 0.2. Which machine would you choose to use? Defend your position If the machine is increasing force then Machine 1. The greater the whole number value, the greater the mechanical advantage.If the machine is increasing distance then machine 2. Although the output force is only a fraction of the input force, the machine
What force causes output work to always be less than input work? Friction force. A portion of all input work is used to overcome frictional force.
Calculate the efficiency of a machine that does 59J of work with an input of 75J. Efficiency = (output work/input work) x 100 (59 J/75 J) x 100=79%
17. How much power does it take to lift 30.0 N 10.0 m high in 5.00 s? P = (30 N)(10 m) / 5 s =60 W
18. A car uses 2,500 Joules in 25 seconds. Find power. P =(2500 J)/25s = 100 W
Be sure to review your simple machines-how they work and examples
how is baseball bat a lever your arms provide a fulcrum and effort as the bat swings.
which item was an inclined plane? the fan blade
how are shoelaces like pulleys
Created by: isaac shapiro