Work • A quantity that measures the effects of a force acting over a distance • Work = force x distance • W = Fd
Work • Work is measured in: • Nm • Joules (J)
Work Example • A crane uses an average force of 5200 N to lift a girder 25 m. How much work does the crane do?
Work Example • Work = Fd • Work = (5200 N)(25m) • Work = 130000 N m = 130000 J
Power • A quantity that measures the rate at which work is done • Power = work/time • P = W/t
Power • Watts (W) is the SI unit for power • 1 W = 1 J/s
Power Example • While rowing in a race, John uses 19.8 N to travel 200.0 meters in 60.0 s. What is his power output in Watts?
Power Example • Work = Fd • Work = 19.8 N x 200.0 m= 3960 J • Power = W/t • Power = 3960 J/60.0 s • Power = 66.0 W
Machines • Help us do work by redistributing the force that we put into them • They do not change the amount of work
Machines • Change the direction of an input force (ex car jack)
Machines • Increase an output force by changing the distance over which the force is applied (ex ramp) • Multiplying forces
Mechanical Advantage • A quantity that measures how much a machine multiples force or distance.
Mechanical Advantage Inputdistance Mech. Adv = Output Distance Output Force Mech. Adv. = Input Force
Mech. Adv. example • Calculate the mechanical advantage of a ramp that is 6.0 m long and 1.5 m high.
Mech. Adv. Example • Input = 6.0 m • Output = 1.5 m • Mech. Adv.=6.0m/1.5m • Mech. Adv. = 4.0
Simple Machines 9.2
Simple Machines • Most basic machines • Made up of two families • Levers • Inclined planes
The Lever Family • All levers have a rigid arm that turns around a point called the fulcrum.
The Lever Family • Levers are divided into three classes • Classes depend on the location of the fulcrum and the input/output forces.
First Class Levers • Have fulcrum in middle of arm. • The input/output forces act on opposite ends • Ex. Hammer, Pliers
First Class Levers Input Force Output Force Fulcrum
Second Class Levers • Fulcrum is at one end. • Input force is applied to the other end. • Ex. Wheel barrow, hinged doors, nutcracker
Second Class Levers Output Force Fulcrum Input Force
Third Class Levers • Multiply distance rather than force. • Ex. Human forearm
Third Class Levers • The muscle contracts a short distance to move the hand a large distance
Third Class Levers Output distance Input Force Fulcrum
Pulleys • Act like a modified member of the first-class lever family • Used to lift objects
Pulleys Output Force Input force
The Inclined Plane • Incline planes multiply and redirect force by changing the distance • Ex loading ramp
The Inclined Plane • Turns a small input force into a large output force by spreading the work out over a large distance
A Wedge • Functions like two inclined planes back to back
A Wedge • Turns a single downward force into two forces directed out to the sides • Ex. An axe , nail
Or Wedge Antilles from Star Wars
Not to be mistaken with a wedgIEEEEE
A Screw • Inclined plane wrapped around a cylinder
A Screw • Tightening a screw requires less input force over a greater distance • Ex. Jar lids
Compound Machines • A machine that combines two or more simple machines • Ex. Scissors, bike gears, car jacks