Simple Machines Device that makes doing work easier is a machine Machines increase applied force and/or change direction of applied force to make work easier

Effort and Resistance Force applied to machine is effort force Resistance force – force applied by machine to overcome resistance

Energy and Simple Machines Amount of energy the machine transfers to the object cannot be greater than the amount of energy transferred to the machine

Energy and Simple Machines An ideal machine with no friction would have the same input work and output work Some energy transferred is changed to heat due to friction

The number of times a machine multiplies the effort force. Mechanical Advantage The number of times a machine multiplies the effort force. MA = Resistance Force Effort Force

Efficiency Measure of how much of the work put into a machine is changed into useful output work by the machine. Efficiency = x 100 out W in

Lever Bar that is free to pivot about a fixed point called the fulcrum MA of lever depends on the placement of the fulcrum

Simple Machines Which lever will allow the weight to be lifted with the least amount of force? fulcrum fulcrum It is easier to lift a weight when the fulcrum is closer to the weight being lifted. 9

Simple Machines Below is a picture of a perfectly balanced system. Describe how mass affects the distance from the fulcrum. 100 g 200 g fulcrum The greater mass is closer to the fulcrum. Notice that is twice as big and half as close. We always measure to the center of mass. 10

Pulley Grooved wheel with a rope or cable running along a groove The greater the number of times the cable wraps around the pulleys, the greater the MA.

Simple Machines Which pulley system will allow the weight to be lifted with the least amount of force? Moveable pulleys, often grouped together in block and tackle systems, reduce the amount of force needed to lift an object. Block and Tackle 12

Wheel and axle Machine with two wheels of different sizes rotating together

Simple Machines Gears are a type of simple machine. While it takes less force to spin the larger wheel, the smaller wheel spins at a faster rate. 14

Inclined Plane Sloping surface that reduces the amount of force required to do work

Which ramp would it be easiest to slide a box up to the given height? Simple Machines Which ramp would it be easiest to slide a box up to the given height? Making ramps longer lowers the amount of force needed to move an object up the ramp. 16

Wedge Inclined plane with one or two sloping sides

Screw Inclined plane wrapped in a spiral around a cylindrical post

Compound machine Uses a combination of two or more simple machines

What force is it that opposes this motion? Efficiency The efficiency of machines can be determined by using a simple formula found on the formula chart. Machines are always less than 100% efficient because of the force that opposes motion between the parts of the machine. What force is it that opposes this motion? Friction opposes the motion in the machines. Friction converts the machine’s work into heat. 20

Formulas W = F x d P = Work/t MA = Resistance Force Effort Force W out Vf = Vi + at d = Vi t + ½ at2 2ad = Vf2 – Vi2 d = ½ (Vf + Vi) t MA = Resistance Force Effort Force W = F x d P = Work/t KE = ½mv2 Efficiency = x 100 out W in GPE = mgh ME = KE + PE