CH 14.1 Work and Power

TrueFalseStatementTrueFalse Work is the product of force, distance and time Power is the amount of work done in a certain time Horsepower, is compared to an actual horse’s power The SI unit for work is the watt The SI unit for power is the joule

Work Work is the product of force and distance Force is unbalanced

Requires Motion Depends on Direction Some of the force must act in the same direction as the object moves No movement = no work Forces act in the same direction as the movement Force that does not act in the direction of motion does not do work on an object Work

Calculating Work SI Units  W= J, joule  F =  d = m How much work is done by a weight lifter who lifts 1600N over his head, at a height of 2m? Given: Formula: Solve:

Power Power- rate of doing work Work at a faster rate = increasing power Increase power  More work in a given time  More work in less time

Calculating Power SI Units  P= W, watt  = 1J per s  W= J  t= s You exert a force of 72N to lift a box to a height of 1m in 2s. How much power is used to lift the box? Give: Formula: Solve:

Math Practice pg

Horsepower  hp = 746 watts James Watts  Comparison of power outputs of steam engines vs output of strong horse

CH Work and Machines

TrueFalseStatementTrueFalse Machines make work easier, by changing force, direction or distance The force you exert on a machine is output force The final product of the machine is called output force Output work is always less than input force due to friction Both force input and force output are equal to force x distance

Machines and Work Machine  A device that changes force  Make work easier by  Changing size of force  Direction of force  Distance over which force acts

Machines and Work Increasing Force  Small force over a large distance = large force over a short distance  Ex-jack Increasing Distance  Decrease applied force by increasing the distance in which the force is exerted Changing Direction  Ex-oar

Work Input Input force-  force you exert on machine Input distance-  distance of input force Work Input-  input force x input distance Friction makes work done by a machine less than the work done on the machine

Work Output Output force-  force exerted by the machine Output distance-  distance of output force Work Output-  output force x output distance

CH Mechanical Advantage and Efficiency

TrueFalseStatementTrueFalse Mechanical advantage is the # of times a machine increases output force IMA is the ideal mechanical advantage, which is only possibly without friction AMA is the actual mechanical advantage, which is output force/input force Efficiency of a machine is the input work that becomes output work Efficiency can never equal 100%

Mechanical Advantage The # of times that a machine increases an input force Ex: Nut cracker  At pivot- 7 times your input force  At middle- 3 times your input force

Actual Ideal IMA is the mechanical advantage in the absence of friction Actual MA is always less than the IMA due to friction Mechanical Advantage AMA is the actual forces acting on a machine

Calculating IMA IMA = Input Distance Output Distance No SI Unit A woman drives her car onto a ramp for repairs. She drives 1.8m along the ramp to raise the car 0.3m. What is the IMA? Given: Formula: Solve:

Math Practice pg

Efficiency The % of work input that becomes work output Due to friction, it is always less than 100% Efficiency= Work Output Work Input X 100% Reduce friction = more efficiency

CH 14.4 Simple Machines

TrueFalseStatementTrueFalse Compound machines contain 2 or more of the 6 simple machines There are 4 classes of levers, that depend where the fulcrum is located A thin wedge has a bigger IMA than a thick wedge A wheel and axle, is composed of 1 wheel, or disk An inclined plane IMA is the height/ the distance

Simple Machines 6 Simple Machines

Lever A ridged bar, free to move around a fixed point Fixed point moves around a fulcrum IMA = input arm/output arm 1 st Class  MA = 1, 1 2 nd Class  MA = > 1 3 rd Class  MA = < 1

Name the Lever

Wheel and Axle 2 disks with different radii IMA = radius of input force/ radius of output force MA = > 1

Inclined Plane Slanted surface along which a force moves an object to difference elevation IMA = distance of inclined plane/ change in height

Wedge V shape, with 2 inclined planes sloped into each other MA = > 1 Thin wedge of a given length has a greater IMA than a thick wedge of the same length

Screw Inclined plane wrapped around a cylinder Closer threads have more IMA than far apart threads

Pulley Rope that fits into a groove in a wheel IMA = # of rope sections supporting the load being lifted Fixed Pulley  Rotate in place  MA = 1 Movable Pulley  Attached to the object being moved Pulley System  Mix of fixed and movable

Name the Pulley

Compound Machines Combination of 2 or more simple machines working together Scissors  Wedge, and lever

Name the simple Machines