Presentation on theme: "Can you tell what this lesson is about ?. WORK! WORK is done on an object when a force is exerted on the object that causes the object to move some distance."— Presentation transcript:
WORK is done on an object when a force is exerted on the object that causes the object to move some distance. There is no work done if the object doesn’t move. Work is only done if the force is exerted in the same direction as the motion.
Force, Motion, and Work The amount of work done on an object depends on the direction of the force and the object’s motion. Work
Amount of Work The amount of work done on an object can be determined by multiplying force times distance. When April lifts a trumpet or a tuba up the stairs, she does work. Work
The amount of work depends on the amount of force exerted and the distance the object moves. To calculate the amount of work done on an object: Work = Force X Distance
Work(J) = Force(N) X Distance(m) Force is measured in Newtons (N) Distance is measured in meters (m) Work is measured in Newton-meters (N. m) One Newton-meter is a Joule (J) One Joule is the amount of work you do when you exert a force of 1 N to move an object a distance of 1 m.
Calculate Work Work = Force X Distance While mowing your yard, you push the lawnmower with a force of 50N for a distance of 20 meters. How much work did you do on the lawnmower? Calculate: Work = Force X Distance Work = 50 N x 20 m Work = 1000 N m Work = 1000 J
Understanding Simple Machines A simple machine is a device that makes work easier by changing the amount of force exerted, the distance the force is exerted, or the direction the force is exerted. A machine does not change the amount of work that is done, it only makes the work easier.
Understanding Simple Machines Using Machines In the picture below, using a ramp makes it easier for April to move the speaker onto the stage. When you use a machine to do work, you exert a force over some distance. The force you exert is called the input force. The input force is exerted over a certain distance, called the input distance. The machine does work by exerting a force over another distance called the output distance. The force the machine exerts is called the output force. The output force is the force you would have to use without the machine. Without a machineWith a machine
Understanding Simple Machines Most machines increase the force that is exerted on them. A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. The ratio of output force to input force is the mechanical advantage of a machine. Mechanical Advantage = Output force Input force Drums are tuned by tightening and loosening bolts. Drum keys make the bolts easier to turn.
Inclined plane Wedge Screw There are 6 types of simple machines: Lever Pulley Wheel and Axle Understanding Simple Machines
Inclined Plane Inclined Plane: An inclined plane is a flat, slanted surface. An inclined plane allows you to exert a smaller input force over a longer distance. A ramp is an inclined plane. The ramp exerts a larger output force over a shorter distance.
Inclined Plane The man is lifting the boxes into a truck bed that is 1 meter high. The ramp is 3 m long. It requires a force of 30 N for the man to push the stack of boxes up the ramp. The boxes weigh 90 N. Compare the amount of work that would be done with and without the ramp. What is the mechanical advantage of the ramp?
Wedge A wedge is two inclined planes placed back-to-back. With a wedge, the inclined plane itself moves. A wedge allows you to exert a smaller input force over a longer input distance. It also changes the direction of the force. Wedge
Screw A screw is an inclined plane wrapped around a cylinder. The threads of a screw act like an inclined plane to increase the distance over which input force is exerted. Screw
Lever A lever is a rigid bar that is free to pivot, or rotate, about a fixed point. The fixed point that a lever rotates around is called the fulcrum. A lever has three parts: input force, output force, and fulcrum. Depending on where these three parts are, levers can increase force, increase distance, or simply change the direction of a force.
Lever Three Classes of Levers The three classes of levers differ in the positions of the fulcrum, input force, and output force.
Types of Pulleys Pulley systems are classified by the number and position of the wheels they contain.
A simple machine made of two connected objects that rotate about a common axis is called a wheel and axle. The object with the larger diameter is called the wheel and the object with the smaller diameter is called the axle. Because the wheel is larger than the axle, a small input force on the wheel is exerted over a long distance. In return, the axle rotates and exerts a large output force over a short distance. Wheel and Axle