Work and machines Making jobs easier Work n

Work and machines Making jobs easier

Work n Work is done on an object when a force is exerted on an object that causes the object to move some distance. No work without motion n No work without force in the same direction n

Motion and force n Person does not work on weights – weights do not move Force on weights http: //www. pricespower. com n Person does work on weights – weights moved Force on weights Summer Olympics 2000 Sydney Australia By Lou Jones

Direction and force n Horse does not work on the rider – force not in same direction Force on person n Horse does work on the cart - force and motion in the same direction Force on cart motion

Calculating work n Work = Force X Distance Force units = Newton, N n Distance units = meter, m n Work units = Joule, J n • J = N*m

Making work easier n Machines Change the amount of force you exert n Change the distance over which you exert force n Change the direction in which you exert force n Do change the amount of work done n

Total work does not change n Work = Force X Distance If a machine allows you to apply a smaller force the distance will increase n If a machine reduces the distance the force will increase n If a machine allows you to apply a force in a different direction it doesn’t change how much force you have to apply or how far you move it n

Mechanical advantage The number of times a force exerted on a machine is multiplied by the machine n Mechanical ad. = Output force Input force n If M. A. > 1 machine increases force needed but distance decreases n If M. A. < 1 machine reduces force needed but distance increases n

Efficiency n Efficiency compares the output work to the input work (%) n n Cannot be greater than 100% Efficiency usually < 100% n Friction

Types of simple machines Inclined plane n Wedge n Screw n Lever n Wheel and axle n pulley n Image taken from: http: //www. daniel-wright. district 103. k 12. il. us/ccheifetz/physics. html

Inclined plane teacher. scholastic. com/dirtrep/ simple/img/plane. gif

Wedge teacher. scholastic. com/dirtrep/ simple/img/wedge. gif

Screw teacher. scholastic. com/dirtrep/ simple/img/screw. gif

Lever teacher. scholastic. com/dirtrep/ simple/img/lever. gif

Wheel and axle teacher. scholastic. com/dirtrep/ simple/img/wheel. gif

Pulley teacher. scholastic. com/dirtrep/ simple/img/pulley. gif