Presentation on theme: "Week 15. Monday Warm Up Week 15 What is work? Cornell Notes: Work and Simple Machines Work: the transfer of energy to an object by using a force that."— Presentation transcript:
Cornell Notes: Work and Simple Machines Work: the transfer of energy to an object by using a force that causes the object to move in the direction of the work. Movement in direction of force.
How do you know if it is work? 1. the object moves as force is applied 2. the object moves in the same direction as the force Ex: carry a backpack (force up, motion forward) not work. lifting a bag (force up, motion up) is work.
How do you calculate work? Work = Force x distance W = F x d Force in Newtons Distance in meters
What is the unit to measure work? Joule (J) Work is a transfer of energy, joules measure energy.
What is power? Power is the rate at which work is done. Power = Work divided by time (P = W/t) Measured in Watts (W)
What is a machine? A device that helps do work by overcoming a force orchanging direction of applied force
What is work input? Work input is the amount of work you do on the machine. Work input is force x distance you put into machine.
What is work output? Work output is the work done by the machine. Work output = Force x distance of output.
How do machines help? 1. They DO NOT increase amount of work done. 2. They DO allow force to be applied over greater distance which means less force is needed to do same work.
Let's find all the ways to get 12 J of work: ForceDistance 121 62 43 34 26 112 As force decreases, distance increases but work stays the same.
What is mechanical advantage? Some machines make work easier by increasing force or giving it a mechanical advantage. Mechanical advantage is the number of times a machine multiples force.
How do you calculate mechanical advantage? mechanical advantage = output force divided by input force. MA = output/input
Thought check: If you had to push a 500 N weight up a ramp and only needed to push with 50 N of force, what is the mechanical advantage of the ramp?
What is mechanical efficiency? The ratio of work output to work input is the mechanical efficiency. Work Output is always less than work input because the machine has to overcome friction.
How do you calculate mechanical efficiency? mechanical efficiency = work output/work input x 100 The ME is expressed as a percentage. A perfect machine would be 100% efficient.
Tuesday Warm Up Week 15 Suppose you exert 60 N on a machine and the machine exerts 240 N on another object. What is the machine's mechanical advantage? MA = output/input
Cornell notes: Simple machines Content/writing space
What are the six simple machines? Levers Pulleys Wheel and axle Inclined Plane Wedge Screw
Lever: A machine that has a bar that pivots at a fixed point called a fulcrum. Input force Output force
Three types of levers: First class lever: fulcrum in middle Second class lever: Output force (load) in middle Third class lever: Input force (effort) in middle
Lever's Mechanical Advantage: MA = output force/input force Second class lever MA > 1 (load close to fulcrum) Third class lever MA < 1 (force decreased but over longer distance) First class lever MA depends upon location of fulcrum.
Pulley: machine that consists of a wheel over which a rope passes. Fixed Pulley Movable Pulley Block and Tackle
Mechanical Advantage of Pulley Fixed: MA = 1 Movable: MA = 2 Block & Tackle: MA = # rope segments on load