Work & Machines
Work Work occurs when a force causes an object to move in the direction of the force. (pg. 70) You’ll know that work is done on an object if two things occur: The object moves as force is applied The direction of the object’s motion is the same as the direction of the force applied Work can be calculated by W = F x d and is expressed in joules (J).
Power Power is the rate at which work is done. (pg. 74) Power can be calculated by P = W/t and is expressed in watts (W). Power is how fast work happens. Power is increased when more work is done in a given amount of time. Power is also increased when the time it takes to do certain amount of work is decreased.
What is a Machine? A machine is a device that helps make work easier by changing force, changing distance, or changing direction of the force you exert. (pg. 77) All machines are constructed from these 6 simple machines: lever, inclined plane, wedge, screw, wheel & axle, & pulley.
Inclined Planes A inclined plane is a simple machine that is a straight, slanted surface. (pg. 85) Inclined planes make work easier, but remember that machines do not save work-therefore, the input must be exerted over a longer distance.
Wedges A wedge is a double inclined plane that moves. (pg. 86) When you move a wedge through a distance, it applies a force on an object.
Screws A screw is an inclined plane that is wrapped in a spiral. (pgs. 87) When a screw is rotated, a small force is applied over the long distance along the inclined plane of the screw. Meanwhile, the screw applies a large force through the short distance it is pushed.
Levers A lever is a simple machine consisting of a bar that pivots at a fixed point, called a fulcrum. (pg. 88) Levers are used to apply a force to a load. There are 3 classes of levers, based on the locations of the fulcrum, the load, and the input force.
Wheel & Axle A wheel and axle is a simple machine consisting of two circular objects of different sizes. (pg. 95) The wheel is the larger of the two circular objects, and the axle is the smaller.
Pulleys A pulley is a simple machine consisting of a grooved wheel that holds a rope or cable. (pgs. 93) A load is attached to one end of the rope, and an input force is applied to the other end. There are two kinds of pulleys: fixed and movable. Fixed and movable pulleys can be combined to form a block and tackle.
Compound Machines Most of the machines in your world are compound machines, machines that are made of two or more simple machines. (pg. 96)