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Laws of Motion and Energy. Chapter Six: Energy and Machines. 6.1 Energy and Conservation of Energy 6.2 Work and Power 6.3 Simple Machines. Investigation 6B. Force, Work and Machines. How do simple machines operate?. 6.3 Simple Machines.
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Chapter Six: Energy and Machines • 6.1 Energy and Conservation of Energy • 6.2 Work and Power • 6.3 Simple Machines
Investigation 6B Force, Work and Machines • How do simple machines operate?
6.3 Simple Machines • A machineis a device, like a bicycle, with moving parts that work together to accomplish a task. What kinds of energy are needed to make this machine work?
6.3 Input and output • To understand how a machine works, think about inputand output. • The input includes everything you do to make the machine work. • The output is what the machine does for you. Output Input
6.3 Input and output • Inputcan be forces, energy, or power supplied to make a machine work. • Output is the forces, energy, or power provided by the machine. Forces Energy Power Forces Energy Power
A simple machineis an unpowered mechanical device, such as a lever. Some other simple machines are a wheel and axle, ropes and pulleys, gears, and a ramp. 6.3 Simple Machines
6.3 Input and output • With a lever, the input force(also called the effort) is the force you apply. • The output forceis the force exerted on the load you are lifting. Output Input
One person can easily lift an elephant with a properly designed system of ropes and pulleys. 6.3 Simple machines
6.3 Work and energy • The output work done by a simple machine can never exceed the input work done on the machine. • Friction always converts some of the input work to heat and wear, so the output work is always less than the input work.
6.3 Real machines and efficiency • The efficiency of a machine is the ratio of work output to work input. Can you calculate the efficiency of this machine?
6.3 Real machines and efficiency • Efficiency is usually expressed in percent. • Because some friction is always present, 100% efficient machines are impossible. • An important way to increase the efficiency of a machine is to reduce friction. • Ball bearings and oil reduce rolling friction. • Slippery materials such as TeflonTM reduce sliding friction. • Designing a car with a streamlined shape reduces air friction.
Cars are not very efficient at using the energy in gasoline. Only 13 % of the energy in a gallon of gas is transformed into output work. 6.3 Real machines and efficiency
6.3 Mechanical advantage and levers • You can make a lever by balancing a board on a log. • Pushing down on one end of the board lifts a load on the other end of the board.
6.3 Mechanical advantage and levers • All levers include a stiff structure that rotates around a fixed point called the fulcrum. • Levers are found in many common machines.
6.3 Mechanical advantage and levers • Mechanical advantageis the ratio of output force divided by input force. • The input and output forces are different if the fulcrum is not in the center. This lever has a mechanical advantage of 3.
6.3 Ropes and pulleys • Ropes and strings carry tensionforces along their length.
6.3 Ropes and pulleys • The mechanical advantage of a pulley system depends on the number of strands of rope directly supporting the load.
6.3 Ropes and pulleys • There are 2 strands of rope supporting this load, so the load feels 2 times your input force.
6.3 Ropes and pulleys • What is the mechanical advantage of a pulley with three strings?
6.3 Gears, ramps and screws • Gears allow rotating speeds to change while power stays constant. • The rule for how two gears turn depends on the numbers of teeth on each.
6.3 Gears, ramps and screws • A ramp allows you to raise a heavy cart with less force than you would need to lift it straight up. • Ramps reduce the input force by increasing the distance over which the input force acts.
6.3 Gears, ramps and screws • A screw is a simple machine that turns rotating motion into linear motion. • A screw works just like a ramp that curves as it gets higher.
Technology Connection A Mighty Energizing Wind • There is a new kind of farm that is unlike any other – it doesn’t produce food - it produces energy from wind.
Chapter Activity Pop Goes the Balloon • Rube Goldberg is well known for creating fun illustrations that show how many simple steps can work together to accomplish something. • For this activity, you will design and build a multi-step device that will pop a balloon.
