Work, YA!!!!!! Finally something easy

1. Work, YA!!!!!! Finally something easy

2. What is work? • As Ice Cube once said ‘Work is ‘bout getting paid yo!” • Luckily for us that’s not what work is, work is how much force and distance is needed to move or do something therefore: • W=f x d where f is force (N) and d is distance in (M), so our units for work are Nm but because people like to make things confusing for you, a Nm is also a joule (J). Named after James. There’s a reason for that…

3. Examples • How much work does Frank do if he lifts a 75N load of rice into the back of his truck 1.4 m off the ground? • W = f x d • W = 75 x 1.4 • W= 105 Nm or 105J

4. Example 2

5. Work at an angle • Sometimes we waste our energy doing work when we’re not parallel to the object we wish to work on. Make sense? EX Pushing a box at an angle means yes the box moves to the direction wanted but some work is wasted up or down, as our desired outcome is to move the box left to right. • We use this new formula: • W= F x D x cos(x) • Where when we break it down like vectors we use the cosine function to find our horizontal work.

6. Example • Mr. Caddy got stuck in mud. He’s pushing on his vehicle at a 27 degree angle with 1000N of force. If I get my truck free and it moves 1.5 meters, how much work is done? • W = f x d x cos(x) • W = 1000 x 1.5 x cos(27) • W= 1336.5 Nm or J • Work and force aren’t the same thing if you drew a triangle just so you know because I made the same mistake!

7. Energy • Energy is: the ability of an object to produce a change in itself or the world around it. • Law of Conservation of Energy: Energy isn’t created or destroyed it simply changes forms. • This means Ebefore=Eafter • You might think WHOA!!! Not true. WRONG it is. It doesn’t mean all energy is useful energy but its still there. • Show that thing from smartboard you have

8. Kinetic Energy • Kinetic Energy: Is the energy of movement, so running requires kinetic energy, a ball rolling has kinetic energy. Get it? Good. • We are able to calculate this energy using a fun formula: • Ke=1/2mv2

9. Example • What is the kinetic energy of a cheetah who has a mass of 104 kg running at 34 m/s? • Ke=1/2mv2 • .5 x 104 x 342 • = 60112J • This stuff isn’t to hard on it’s own. Shortly I’ll take it hard because I’m THAT guy.

10. To add to that point • Although this isn’t required by BC to get learned it makes sense so I’m teaching it. • Work is also defined as the change in kinetic energy. How so you ask? Good question. • Because work requires velocity or movement, whenever something moves or changes it requires work. Because movement is kinetic energy this should all make sense. So work: • W = ∆Ke (because it’s a change its final – initial)

11. Example • How much work would be required to slow down a bear charging at you if the mass was 109kg and he was running at 17 m/s? • W = (1/2mv2f) - (1/2mv2i) • W= .5x109x0 - .5x109x172 • W= 15750.5J or Nm • Lets try some in our text on 261

12. Work and graphs • You’ll see again it’s possible to graph the work we do. Simply stated force goes on the y axis and distance on the x. • On the next slide I’ll show how easy it is. It’s easy as 3.14

13. Graphical Method of Finding Work • Compare the Formula for Area and Work A = L x W W = F x d 10m 10 N W = F x d W = 10N x 4m W = 40 N·m W = 40 J A = L x W A = 10m x 4m A = 40m2 Length (m) Force (N) Width (m) Distance (m) 4 m 4 m

14. Graphing continued • So basically it’s just like when we found displacement and such from our vt graphs.

15. Gravitational Potential Energy • GPE: (writing it out so long!) is energy that we have due to the earth’s gravitational pull, our mass and a height. This should make sense because by definition of work, energy is required to move things. Use example • Ep= mgh • Ep= gravitational potential energy (J) • m = mass (kg) • g = acceleration due to gravity (9.80m/s2) • h = height (m)

16. Example • A picture with a mass of 3.8kg hangs on a wall 2.1m above the ground. What is the gravitational potential energy of the picture relative to the floor? • Ep = mghEp= (3.8kg)(9.80m/s2)(2.1m) • m = 3.8kg • g = 9.80m/s2Ep = 78.2J • h = 2.1m

17. Putting this stuff together example • A 65.0 kg pole vaulter runs along a track at a speed of 7.9 m/s, which gives him kinetic energy of 2.03 x 103 J. Using the pole to change the direction of his motion, he lifts himself up a height of 3.68 m in the air—an Olympic-level performance. • (a) How much potential energy does the vaulter gain at the top of his vault?

18. Other types of energy & stuff • Temperature: is a measurement of the average kinetic energy of the molecules in an object or system and can be measured with a thermometer. It is a means of determining the internal energy contained within the system. • Thermal Energy: A measure of internal motion of an objects particles. (always tries to equalize from hot to cold) • Specific heat capacity: the amount of heat it takes to raise the temperature of a 1g substance by one degree Celsius

19. Specific Heat Capacity • The property of water that gives it the ability to moderate the temperature of both the environment and living bodies is its HEAT CAPACITY • Absorption of heat is dependent in the specific heat capacity of the surface

20. Which area of Alberta has air with high specific heat capacities? • Those near large bodies of water • How can you tell? • Because of the smaller differences between day time and night time temperatures

21. What about Calgary? High or low specific heat capacities? • LOW – Temperature is quite dry, therefore they have large temperature swings between day and night

22. FORMULA: Q = mc∆T • C = Specific Heat Capacity (J/goC) • Table on pg318 • Q = Amount of Heat (J) • m = Specific Mass (g) • ∆T = Change in temperature (oC)

23. Question 1: • Suppose you want to make some soup, and you need to heat 500g of water from 10.2oC to 98.7oC. Calculate the amount of heat required to do this. m = 500g c = 4.19 J/goC T = 98.7 – 10.2 = 88.5oC Q = ?

24. Q = mc∆T Q = (500g)(4.19J/goC)(88.5oC) Q = 185407J Q = 1.85x105J

25. Question 2: • Suppose you use a 0.40kg stainless steel pot to warm 2.0kg of water from 12oC to 38oC. Calculate the heat required to warm the water and the pot. The specific heat capacity of the stainless steel is 0.510J/goC.

26. m = 0.4kg = 400g (pot) m = 2.0kg = 2000g (water) T = 38oC - 12oC = 26oC C = 0.510J/goC (pot) C = 4.18J/goC (water) Q = ? (pot) Q = ? (water)

27. Q (pot) • Q = mc∆T • Q = (400g)(0.510J/goC)(26oC) • Q = 5304J

28. Q (water) • Q = mc∆T • Q = (2000g)(4.19J/goC)(26oC) • Q = 217880J • Qtotal = 5304J + 217880J = 223184J • Q = 2.2x105J

29. Temperature Stuff • Absolute zero= the coldest temperature possible ever, -273.5 degrees Celsius • Three types of temp measure: Kelvin (K), Celsius(C) and Fahrenheit(F). • Conversions: • K to C: K – 273 • C to K: C + 273

31. Types of heat transfer • Conduction: Contact between particles (IE rod in a flame) • Convection: A mixture of heat because of a flow. IE boiling water hot and cold continually mix. • Radiation: The transfer of energy through electromagnetic waves. • Examples now on 319.