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MACHINES

MACHINES. Chapter 8, Sections 2. What is a machine?. a device that makes work easier by changing the size or direction of a force. Imagine trying to change a tire without a jack or tire iron Everyday machines: Wheel chair Chopsticks Scissors. Work and Machines.

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MACHINES

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  1. MACHINES Chapter 8, Sections 2

  2. What is a machine? • a device that makes work easier by changing the size or direction of a force. • Imagine trying to change a tire without a jack or tire iron • Everyday machines: • Wheel chair • Chopsticks • Scissors

  3. Work and Machines • Work Input: the work that you do on a machine • You apply an input force through a distance on a machine. • Work Output: the work done by the machine • The machine applies an output force through a distance • Example: We use a can opener to help open a jar. What is the input? What is the output?

  4. Why do machines make work easier? • Work output is ALWAYS less than work input. • Machines do not make work less, just EASIER. • Machines allow force to be applied over a greater distance, which means less force is needed to do the same work. • EX: when loading something into a truck. If you push it up a ramp it will be easier. You need less force but must go a farther distance.

  5. Why is work output always less than work input? • All machines have moving parts that create friction as they move. • SO: some work input always goes into overcoming friction in the machine therefore reducing the work output.

  6. What is the relationship between force and distance in a machine? • Machines change the size and/or direction of the input force. BUT the same work is done with or without the machine. • When using a machine… • Force or distance will increase but NOT both. • Figure 3, p.218 • In the ramp example, the force needed to move the box decreases but the distance it needs to move increases

  7. Mechanical Advantage • The number of times the machine multiplies the force. • Compares input and output force • MA = output force / input force • MA > 1 means the machine makes lifting or moving a heavy object easier. • MA < 1 means the machine can still help, it just reduces the output force.

  8. Mechanical Efficiency • A comparison of a machines work output to its work input. • ***the less work a machine must do to overcome friction, the more efficient it is. • ME = (work output/work input) x 100 • Your answer will be a precentage • Ideal efficiency would be 100% • However due to friction this cannot be done. • What can be done to REDUCE friction? • Use lubricants such as oil or grease

  9. Work Input = Fi x Di Work Ouput = Fo x Do Effort Force = 800 N 2000 N 3 meters 1 meter

  10. Calculating Advantage and Efficiency • Efficiency = (Work Output/Work Input) x 100 • E = (2000/2400) x 100 • E = 0.83 x 100 • E = 83.3 % • Mechanical Advantage = Force Output/Force Input • MA = 2000N/800 N • MA = 2.5

  11. Types of Simple MachinesChapter 8, Section 3 Lever Pulley Wheel and Axle Inclined Plane Wedge

  12. Machines Help us in 3 Ways The machine may: Multiply the input force by increasing the input distance Meaning you use less force but more distance – the machine uses more force and less distance Multiply the input distance by increasing the input force Meaning you use more force and less distance – the machine uses less force and more distance Change the direction of the input force

  13. The Pulley • A machine that consists of a grooved wheel that holds a rope or cable. • A load is attached to one end of the rope, an input force applied to the other end.

  14. Fixed Pulley • This pulley is attached to something that does not move. • It changes the direction of the input force. • Pulling down on the rope pulls the load up.

  15. Movable Pulley • This pulley is attached to the object being moved. • It does NOT change the direction of the force • It increases force by increasing the distance the work is done over.

  16. Block and Tackle Pulley • When a fixed pulley and a moveable pulley are used together. • The mechanical advantage depends on the number of rope segments.

  17. Wheel and Axle • Consists of two circular objects of different sizes • MA = radius of wheel / radius of axle • MA >1 means the radius of the wheel is larger than the axle. • Multiplies input force!

  18. Inclined Plane • straight, slanted surface that helps us to do work. • Multiplies input force by spreading the work over a greater distance! • MA = length of ramp / height of ramp • The greater the ratio the greater the mechanical advantage

  19. The Wedge • A type of inclined plane. • Consists of a pair of inclined planes that move. • Applies an output force that is greater than the input force, but the input force is over a greater distance.

  20. Screw • An inclined plane wrapped around a cylinder. • Applies a small input force over a long input distance. • This increases output force but decreases distance.

  21. The Lever • A simple machine that consists of a bar that pivots at a FIXED point, called a fulcrum. • There are 3 types…

  22. 1st Class Lever • The fulcrum is between the input force (you) and the load (the work to be done) • This lever changes the direction of the input force • It may also increase force OR distance depending on the location of the fulcrum. Effort Load Fulcrum

  23. 2nd Class Lever • The load is between the fulcrum and the input force. • This lever does NOT change the direction of the input force. • Allows you to apply less force over a longer distance. • Multiplies input force! Effort Load Fulcrum

  24. 3rd Class Lever • The input force is between the fulcrum and the load. • Does NOT change the direction of the input force or increase the size of the input force. • Allows for a small input distance but a large output distance. • Reduces input force in exchange for a greater output distance. Load Effort Fulcrum

  25. Compound Machine • A machine made up of two or more simple machines.

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