1. Unit 6 – Lecture 1

2. Work Work = force applied over a certain distance [force and distance are in the same direction] W = F * d Force (F) is measured in Newtons Distance (d) is measured in meters Work = N*m – AKA: Joules (J) NOTE: If the object does not move in the direction of the force, NO WORK IS ACCOMPLISHED.

3. Practice: W = F * d How much work is accomplished by moving a 600N crate 7 m? How much work is accomplished by a 4500N piledriver falling 25 m? How far do you have to push a 300 N crate to accomplish 6000 J of work? What is the force applied to accomplish 20 Joules of work over a 50 meter distance? How much work is accomplished by an 80 N person walking 10 m upstairs? 4200 Joules 112,500 Joules 20 meters 0.4 Newtons 800 Joules

4. Power Power is a rate of the amount of work per second. P = W / t Work is measured in Joules [Newton meters] time is measured in seconds P = Joules/second [power is measured in watts]

5. Practice Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over her head (approximately.60 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds. Which student does the most work? Which student delivers the most power? Neither [same] Ben [takes less time]

6. Practice How much power will it take to move a 10 kg mass at an acceleration of 2 m/s 2 a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order. Just to help you out… F = m * a W = F * d P = W / t F = 10 * 2 F = 20 N W = 20 * 10 W = 200 Joules P = 200/5 P = 40 watts

7. Machines Machines are devices that make work easier. They can do this by: Redirecting a force Multiplying a force Both redirecting & multiplying a force

8. Work & Machines Machines have: a Work Input (W IN ) and a Work Output (W OUT ). in an “ideal” machine, these would be equal.

9. Work & Machines – cont’d Work Input: the effort force multiplied by the effort distance Effort Force (F e ) [aka Input Force (F i )] = the force you put into a machine Effort distance (d e ) = the distance the machine moves because of the effort force W IN = F e * d e

10. Work & Machines – cont’d Work Output: the resistance force multiplied by the resistance distance Resistance Force ( F r ) [aka Output Force (F o )] the force applied by the machine to another object Resistance Distance (d r ) = the distance the machine moves the object because of the resistance force W OUT = F r * d r

11. Work & Machines – cont’d There is an inverse [opposite] relationship between the work which is done by a person and that done by the machine. In normal operations, the person using the machine moves the machine with little force (F e ) through a large distance (d e ). The machine moves an object with a large force (F r ) over a small distance (d r ). In essence, you are moving the machine an extra distance so the machine will apply extra force.

12. Practice What force do you apply to a machine? How far does the machine move another object? Which components comprise the Work Output? Which of these do YOU increase on a machine? effort distance, effort force, resistance distance, resistance force Which of these does the machine increase? effort distance, effort force, resistance distance, resistance force

13. Mechanical Advantage Mechanical Advantage – the number of times the machine multiplies the force you have applied to it. [your force * MA = the output force] MA = F 0 / F i Because we put force above and below, there are no units for MA. It is a number (coefficient) showing how many times the force is multiplied.

14. Efficiency Efficiency – work output divided by the work input efficiency = (W OUT / W IN ) * 100 will be expressed as a percentage HONORS ONLY

15. Practice MA = F o / F i What is the mechanical advantage of a machine that applies 35 N for the 25 N of force put into it? What is the MA of a machine that applies 100 N for the 15 N of force put into it? What is the Force Output of a machine with a MA of 12 when you put 9 N of force into it? 1.4 6.7 108 N

16. Machines A Simple Machine accomplishes the work in one motion. A Compound Machine is made up of two or more simple machines. Most machines are compound machines.

17. Simple Machines There are six types of simple machines: Lever Wheel-and-Axle Pulley Inclined Plane Wedge Screw

18. Homework Complete Work I and Work II worksheets