1. Intro to Agriculture AAEC – Paradise Valley Spring 2015
Work & Power
Intro to Agriculture
AAEC – Paradise Valley
Spring 2015

2. 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.

3. 1.  Work = __________ x _____________
2.  Work is measure in newton-meters, also called the ___________________

4. Work (joules) = Applied force (Newtons) x distance (meters)
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?

5. You can reduce the amount of force needed by increasing the distance.
W is the same in both pictures (225J), though it is easier to move the box using a ramp

6. Power (watts) = work (joules) / time (sec)
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 10m 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 POWER.

7. 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 500W, how long will it take the motor to do 1000 J of work.

8. Power & Energy
Power can also be calculated by measuring how much energy is transferred divided by time. 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?
P = E/t

9. 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

10. How many machines can you count?

11. Input and Output Forces
Input force Fin = force applied to
the machine
Output force Fout  = force applied
by the machine
Fin
Fout

12. Identify the input and output forces.

13. *What happens when you let a car run out of oil?
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?

14. 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 of _________

15. 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

16. SHOW WHAT
YOU KNOW!!!

17. 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: _______
6.  Lightbulbs convert electrical energy into: __________

18. Please Answer the Questions below on a Separate Sheet of Paper, Turn in the Front when you are done.
7. Sarah moves a 3kg box 3 meters. Ira moves a 3kg 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 the contraption they used. _____________