WORK POWER Intro to Agriculture AAEC Paradise Valley

WORK & POWER Intro to Agriculture AAEC – Paradise Valley Spring 2015

WHAT IS WORK? ? ? In physics, work is a transfer of energy when a force makes an object move. Movement must be in the direction of the force. Ex: You pick up the books, they move a distance from the floor.

1. Work = _____ x _______ 2. Work is measure in newton-meters, also called the __________

CALCULATING WORK W = Fd Work (joules) = Applied force (Newtons) x distance (meters) Practice Problems: 1. A bookshelf is pushed with a force of 35 N and moves a distance of 5 m. How much work was done on the couch? 2. A lawn mower is pushed with a force of 150 N, if 12, 500 J of work is being done to mow the lawn, what is the total distance covered by the mower?

YOU CAN REDUCE THE AMOUNT OF FORCE NEEDED BY INCREASING THE DISTANCE. W is the same in both pictures (225 J), though it is easier to move the box using a ramp

WHAT IS POWER? ? ? P = W/t Power (watts) = work (joules) / time (sec) Power measures the time it takes to do work. Suppose you and your friend move boxes that weigh 50 kg each. You both move the boxes 10 m but your friends moves it in 5 seconds and you move it in 3 seconds. You have both done the same amount of work, but you had more

P = W/t PRACTICE PROBLEMS 1. In lifting a brick, 50 J of work are done. How much power is needed if the brick is lifted for 5 seconds. 2. If a runner's power is 100 W, how much work is done by the runner in 20 seconds. 3. If a runner's power is 100 W, how much work is done by the runner in 2 minutes? 4. The power produced by a motor is 500 W, how long will it take the motor to do 1000 J of work.

POWER & ENERGY Power can also be calculated by measuring how much energy is transferred divided by time. P = E/t Power (watts) = Energy transferred (joules) / time (sec) *A 100 W lightbulb converts electrical energy into light (and heat at a rate of 100 J/s) 1. A 60 watt bulb is left on for 20 seconds, how much energy is transferred during this time?

WHAT IS A MACHINE? A device that helps transmit power, force, and motions. Machines do work. Examples of machines: § Scissors § Wheelbarrow § Doorknobs § Axe § Rake § Ramp

How many machines can you count?

INPUT AND OUTPUT FORCES Input force Fin = force applied to the machine Output force Fout = force applied by the machine Fout Fin

Identify the input and output forces.

IDEAL MACHINES Workin = Workout with no loss due to heat (from friction) Mechanical Advantage = output force (newtons) input force (newtons) Efficiency = how much work put into the machine is changed into useful energy, most machines can be made more efficient by reducing friction *What happens when you let a car run out of oil?

1. The lever gave Professor B a mechanical _______ 2. Mechanical Advantage = output divided by ______ 3. The inclined plane is less efficient due to the force

PERPETUAL MOTION MACHINE – A machine that can continue to do work indefinitely without drawing energy from some external source; IMPOSSIBLE under the law of conservation of energy. Commonly refers to any device or system that perpetually (indefinitely) produces more energy than it consumes, resulting in a net output of energy for indefinite time

SHOW WHAT

PLEASE ANSWER THE QUESTIONS BELOW ON A SEPARATE SHEET OF PAPER, TURN IN THE FRONT WHEN YOU ARE DONE. 1. Work measures how much _____ is transferred. 2. Write the equation for work: _____ 3. Work is measured in what unit? _____ 4. Power is measured in what unit? _____ 5. In an ideal machine, Work (in) should equal: _______

PLEASE ANSWER THE QUESTIONS BELOW ON A SEPARATE SHEET OF PAPER, TURN IN THE FRONT WHEN YOU ARE DONE. 7. Sarah moves a 3 kg box 3 meters. Ira moves a 3 kg box 6 meters. Who has done the most work? _____ 8. A machine that continues to work without adding additional energy is called a _____ motion machine. 9. How can you make a machine more efficient? 10. Any device that makes work easier is called a: ______ Extra: In the OKAY GO video, what was the name of