Simple Machines

5.2

SIMPLE MACHINES: ease load, changing either magnitude or direction of a force

WORK input<WORK output

FORCE exerted<FORCE machine

LEVER Simple Lever Pulley Wheel and axle

INCLINED PLANE Simple Inclined Plane Wedge Screw

The Lever Family!EXAMPLES Claw hammer Crowbar See-saw A bar that is free to pivot or turn at a

fixed point. -Fixed point=Fulcrum-Input Arm=Distance from the fulcrum to where the input force is.-Output Arm=distance from the fulcrum to the output force.

Three classes 1st class lever: Claw hammer, the fulcrum

is located in the middle of the arm.

2nd class lever: The fulcrum is located at the end of the arm, output force is b/t input force and fulcrum: A wheelbarrow.

3rd class lever: The fulcrum is located at an end of the arm, the input force is applied b/t the output force and fulcrum.

Pulleys Pulleys are modified levers. Fixed Pulley-change direction of the input

force Movable Pulley- increase input force. Axel = Fulcrum

Depending on the number and arrangement of pulleys, the mechanical advantage is different.

Fr=Fe Mechanical Advantage =1 w/ 1 fixed pulley

Block and Tackle-System w/ fixed and movable.

Wheel and Axle Axle in the center of the wheel

Inclined planes Inclined planes - multiply and redirect forces. Wedge

- is a modified inclined plane Screw

- is an inclined plane wrapped around a cylinder.

Compound Machines Two or more simple machines

Using Machines Increase Force Change Direction Make Work Easy

INPUT FORCE-Force applied to the machine OUTPUT FORCE-Applied by the machine

Mechanical Advantage= Ratio Output Force/Input Force

Fresistance/Feffort

Ideal Mechanical Advantage (IMA)=equal to the displacement of the effort force divided by the displacement of the load.

Fr/Fe=de/dr

Efficiency (%) = Output Work/Input Work x 100% MA/IMA x100

Practice Problem:1.) You examine the rear wheel on your bicycle. It has a radius of 35.6

cm and has a gear with a radius of 4 cm. When the chain is pulled with a force of 155 N, the wheel rim moves 14 cm. The efficiency of this part of the bicycle is 95%.

A. What is the IMA of the wheel and gear: 4 cm/35.6 cm=0.112

B. What is the MA of the wheel and gear: e=ma/IMAx 100 MA=e/100 xIMA (95/100) 0.112= 0.106

C. What is the resistance force: MA=Fr/fe Fr=Max Fe 0.106(155)=16.4

D. How far was the chain pulled to move the rim 14 cm: IMA=de/dr de=IMA x dr 0.112(14)=1.57 cm

2. A sledgehammer is use dto drive a wedge into a log to split it. When the wedge is driven 0.2 m into the log, the log is separated a distance of 5 cm. A force of 17000 N is needed to split the log and the sledgehammer exerts a force of 11000.

a. What is the IMA of the wedge?

(4)a. What is the MA of the wedge?

(1.5)a. Efficiency?

(38%)

Impulse Average force times time Ns F=ma….

Momentum Mass times velocity Kg m/s Vector

Impulse Momentum Theorem Impulse is the change in p

CONSERVATION OF MOMENTUM: pi=pf