Simple Machines & Energy

Transcription

1 Simple Machines & Energy SPS8. Students will determine relationships among force, mass, and motion. e. Calculate amounts of work and mechanical advantage using simple machines.

2 Our use of machines Machines multiply and redirect forces, giving us the benefit of a. There are 6 simple machines that you need to know:

3 Levers

4 3 Classes of Levers

5 First Class Lever The (fixed pivot point) is located between the and the Forces. Example:. The effort and the resistance move in directions. The moves down in order to lift the.

6 First Class Levers When the is closer to the effort than to the resistance, there is a loss in but a gain in. When the fulcrum is closer to the than to the effort, there is a loss in, but a gain in. When the fulcrum is midway between the effort and the resistance, there is in force, speed or distance. Examples of First Class Levers:

7 2 nd Class Levers The is between the effort and the fulcrum. The fulcrum is at one end of the lever. The fulcrum is usually closer to the. Second class levers produce a gain in. Examples of Second Class Levers:

8 3 rd Class Lever The is between the resistance and the fulcrum. There is usually a loss in, but a gain in. Samples of Third Class Levers :.

9 Pulleys A pulley is a grooved wheel that turns around an axle (fulcrum), and a rope or a chain is used in the grove to lift heavy objects. A pulley changes the of the instead of lifting up, you can pull down using your body weigh against the (what you are lifting). A pulley may be,, or.

10 Pulleys A simple pulley doesn t gain force, distance or speed, but it changes the. A fixed pulley (attached to something that doesn't move such as the ceiling or wall) acts like a first class lever with the fulcrum located at the axis; instead of a bar the pulley uses a rope. A moveable pulley acts as second class lever, the is between the fulcrum and the effort. Samples of pulleys:

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12 Wheel & Axle The wheel and axle was first used around 3000 B.C. and is one of the most important invention in history. The wheel and axle is a wheel connected to a rigid pole. The wheel and axle is basically a modified lever, the center of the axle serves as a fulcrum making the wheel a lever that rotates in a circle. Effort force is applied to a large wheel to turn the smaller axle. Samples of wheel and axle -

13 Wheel & Axle Gears are a modified or special wheel and axle. Samples of gears bike sprockets, can opener, gears in any machine.

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15 Inclined Plane An inclined plane is a sloping surface used to lift heavy loads with little effort. The incline plane does not. An inclined plane gives less but the same or more. The trade off is greater to travel. It allows you to lift a weight you normally couldn't lift to a higher level. It increases the elevation of heavy objects without having to lift the object directly. Samples of Inclined Planes:

16 Inclined Planes

17 Wedges A wedge is a form of the which is used to increase force. With a wedge, the material remains in place while the wedge moves through it. A wedge can be one sloping surface, a inclined plane, like a doorstop or two sloping surfaces, a inclined plane, like the wedge used to split wood for the fireplace. Wedges can be forced between two things to hold them tightly together, like nails or a doorstop. When sharpened the wedge becomes either a or and. The tip of a Screwdriver (other than Philips) is a simple wedge. Wedges can be used to, or. Samples of wedges:

18 Wedges

19 Screws A screw is an wrapped around a post. It consists of 2 parts: body and inclined plane. If you look closely at the screw, you'll see that the threads form a tiny ramp that runs around the screw from the tip to near the top. The of a screw is the distance between two consecutive threads. One function of the screw is to fasten things the standard screw or nuts & blots. Drill bits are screws used to make holes; a jackscrew is used to lift heavy objects, i.e. car jack. Airplane propellers, helicopter blades, fan blades and boat propellers are all screws.

20 Compound Machines Any combination of 2 or more simple machines is defined as a. In fact, most machines are compound machines. Some examples are a pair of scissors and a bicycle. Compound machines can do more difficult jobs than simple machines alone. Their is far greater, too.

21 Mechanical Advantage A quantity that measures how much a machine the force or distance Simply put: how much the machine the work we have to do!

22 Mechanical Advantage The mechanical advantage value must be greater than. This tell us if the machine is worth using or not. Mechanical advantage = distance/ distance Use when you re looking at distance Mechanical Advantage = force/ force Use when you re looking at force There are no units for mechanical advantage!

23 Mechanical Advantage: Lever The mechanical advantage of a lever is the distance from the effort to the fulcrum divided by the distance from the fulcrum to the load MA = Distance, effort - fulcrum Distance, load - fulcrum For our example, MA = 10/5 = 2 Distance from effort to fulcrum: 10 feet Distance from load to fulcrum: 5 feet

24 Mechanical Advantage: Pulley The Mechanical Advantage of a pulley is equal to the number of ropes supporting the pulley So for the pulley system shown there are 3 ropes supporting the bottom pulley MA = 3 This means that if you pull with a force of 20 pounds you will lift an object weighing 60 pounds

25 Mechanical Advantage: Wheel and Axle The mechanical advantage of a wheel and axle system is the radius of the wheel divided by the radius of the axle MA = Radius of Wheel Radius of Axle So for our wheel and axle MA = 10 /2 = 5 10" 2"

26 Mechanical Advantage: Inclined Plane The mechanical advantage of an inclined plane is the length of the slope divided by the height of the plane, if effort is applied parallel to the slope MA = Length of Slope Height of Plane So for our plane MA = 15 feet/3 feet = 5 Let s say S = 15 feet, H = 3 feet

27 Mechanical Advantage: Wedge Much like the inclined plane, the mechanical advantage of a wedge is the length of the slope divided by the width of the widest end MA = Length of Slope Thickness of Widest End So for our wedge, MA = 6 /2 = 3 They are one of the least efficient simple machines 2" 6"

28 Mechanical Advantage: Screw The mechanical advantage of a screw is the circumference of the screwdriver divided by the pitch of the screw The pitch of the screw is the number of threads per inch MA = Circumference of Screwdriver Pitch of Screw

29 Diam.=1" 10 threads per inch Circumference = x 1 = 3.14 Pitch = 1/10 = 0.1