Work Work is done when a force moves an object over a distance Work = force X distance or W = f X d When a force is applied to an object, the force may or may not cause the object to move. If the force does not produce motion, NO WORK IS DONE! A force results in work ONLY if motion is produced.
Machines AA device that transfers mechanical energy from one object to another MMake work easier to perform by: 11) multiplying force 22) changing the direction or the distance over which a force is applied EEx: a wrench multiplies applied force when moving a tight bolt. EEx: a loading ramp attached to the back of the truck reduces the force but increases the distance the object must be moved.
Resistance and Effort Resistance = the force a machine has to overcome Effort = the force applied Using a machine CAN reduce the amount of effort needed to overcome a given amount of resistance but a machine does NOT decrease the amount of work
Work Ex: Suppose you lift a box weighing 450 Newtons up onto a 2 meter high platform. To light the box straight up by yourself, you would need to apply 450 Newtons of force over a distance of 2 meters. W= f x d = 450 N x 2 m = 900 J
Work HOWEVER, if you set up a rope and pulley system to change the direction and distance of the force required, you might have to pull in 9 meters of rope only using 100 Newtons of force: W= f x d = 100 N x 9m = 900 J So the TOTAL amount of work is the SAME using the pulley versus not using the pulley
6 Simple Machines Lever Pulley Wheel and axle Inclined plane Wedge Screw
Lever Consists of a rigid bar that can turn around a point called a fulcrum Ex: pliers, crowbar
Pulley AA modified form of a lever. Can change direction of force or decrease the force needed to move a heavy object. EEx: clothes line
Wheel and axle A modified form of a lever. Consists of a large wheel with a smaller wheel (or axle) in its center. They are connected so they turn together. Turning the outer wheel uses less force but must turn a greater distance. Ex: bicycles, car steering wheels, doorknobs
Inclined plane A flat surface with one end higher than the other. Ex: wheelchair ramp, truck ramp
Wedge Double-sided inclined plane. The effort force is applied by driving the wedge into something, like an ax into a log. Ex: ax, knives, wood nails, chisels
Screw An inclined plane wrapped around a wedge or cylinder Ex: wood screws, bolts, car jacks
Complex Machines Contains 2 or more simple machines Ex: a bike has a wheel and axle, a pulley system and a lever.
Efficiency of machines Machines are never 100% efficient The amount of work done by any machines is ALWAYS less than the amount of work put into it Some work is converted into heat energy and is wasted. Heat energy is produced because of rubbing together of the machine’s parts (friction).
Machine efficiency A machine can be made more efficient by reducing friction. Grease oil, and wax are good ways to reduce the friction between moving parts. Sanding surfaces to make them smoother or using ball bearings between surfaces also reduces friction.