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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. 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). Ohhh Pretty!!!! James Prescott Joule (24 December 1818 – 11 October 1889) was an English physicist and brewer (maker of beer – yum yum). Born in Salford, Lancashire (North West England). Joule studied the nature of heat, and discovered its relationship to mechanical work - i.e ENERGY. James Joule How much work does Esther do if she lifts a 75N load of rice into the back of her vehicle1.4 m off the ground? W=fxd W = 75 x 1.4 W= 105 Nm or 105J 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 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. Mr. Willard got stuck in mud. He’s pushing on his vehicle at a 27 degree angle with 1000N of force. If I get my car free and it moves 1.5 meters, how much work did I put into the situation? W = f x d x cos(x) W = 1000 x 1.5 x cos(27) W= 1336.5 Nm or J 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 Einitial=Efinal Kinetic Energy: Is the energy of movement, so running requires kinetic energy, a ball rolling has kinetic energy. We are able to calculate this energy using a formula: Ke=1/2mv2 What is the kinetic energy of a cheetah who has a mass of 104 kg running at 34 m/s? Ke=1/2mv2 Ke = ½ x 104 x 342 Ke = 60112 J This stuff is easy, right? 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) W = KEf-KEi 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= .5 x 109 kg x 0 m/s - .5 x 109 kg x 17m/s2 W= 15750.5 J or Nm 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. Compare the Formula for Area and Work A=LxW W=Fxd 10m Length (m) 10 N W=Fxd A=LxW Force (N) A = 10m x 4m W = 40 N·m W = 40 J A = 40m2 Width (m) W = 10N x 4m 4m Distance (m) 4m Gravitational Potential Energy - ughhhh, writing it out so long! Just use GPE or PE. GPE: 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. Ep = mgh WHERE: Ep = gravitational potential energy (J) m = mass (kg) g = acceleration due to gravity (9.80m/s2) h = height (m) 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 = mgh m = 3.8kg g = 9.80m/s2 h = 2.1m Ep = (3.8kg)(9.80m/s2)(2.1m) Ep = 78.2J 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 Specific heat capacity is the amount of heat energy required to raise the temperature of a substance per unit of mass. Heat Capacity Symbol: ‘C’ is the amount of heat in joules required to raise 1 gram or kg of a substance 1 degree celsius. Water’s specific heat capacity is 4.18 J/g °C or 4180 J/kg °C C = Specific Heat Capacity (J/goC) Q = Amount of Heat (J) m = Specific Mass (g) ∆T = Change in temperature (oC) 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 (specific heat capacity of water) T = 98.7 – 10.2 = 88.5oC Q=? Q = mc∆T Q = (500g)(4.19 J/goC)(88.5oC) Q = 185407 J Q = 1.85x105 J 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. m = 0.4kg = 400g (pot) m = 2.0kg = 2000g (water) T = 38oC - 12oC = 26oC C = 0.510 J/goC (pot) C = 4.18 J/goC (water) Q = ? (pot) Q = ? (water) Q = mc∆T Q = (400g)(0.510J/goC)(26oC) Q = 5304J Q = mc∆T Q = (2000g)(4.19J/goC)(26oC) Q = 217880J Qtotal = 5304J + 217880J = 223184J Q = 2.2x105J 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 Conduction: Contact between particles. IE candle and 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.