1 00:00:00,000 --> 00:00:02,000 It takes energy to do work. 2 00:00:02,000 --> 00:00:04,000 Energy comes in a variety of forms. 3 00:00:04,000 --> 00:00:07,000 The powder in this funnel has potential energy. 4 00:00:07,000 --> 00:00:10,000 It's changed into heat energy when I blow it through this flame. 5 00:00:14,000 --> 00:00:18,000 If I do work and use my energy to stretch this giant slingshot, 6 00:00:18,000 --> 00:00:22,000 the energy is stored as elastic potential energy. 7 00:00:22,000 --> 00:00:27,000 And when I let go, the energy is changed into energy of motion, or kinetic energy. 8 00:00:28,000 --> 00:00:29,000 Finally! 9 00:00:30,000 --> 00:00:32,000 Flexiglass did the work to stop the tomato. 10 00:00:33,000 --> 00:00:36,000 It takes a lot of work to lift this 25-kilogram anvil. 11 00:00:36,000 --> 00:00:38,000 I have to overcome the pull of gravity. 12 00:00:38,000 --> 00:00:42,000 The anvil now has a lot of gravitational potential energy. 13 00:00:42,000 --> 00:00:47,000 This poor cantaloupe will be smashed when I release the energy by letting go. 14 00:00:53,000 --> 00:00:54,000 Hi, Dr. D. 15 00:00:54,000 --> 00:00:56,000 That was a great show. 16 00:00:56,000 --> 00:00:58,000 I really like the experiments. 17 00:00:58,000 --> 00:00:59,000 Thanks. 18 00:00:59,000 --> 00:01:01,000 By the way, are you working on any projects? 19 00:01:01,000 --> 00:01:03,000 Well, Jacob has broken his foot, 20 00:01:03,000 --> 00:01:07,000 so we're trying to figure out a way to get him back into the treehouse. 21 00:01:07,000 --> 00:01:10,000 We think we can lift him with a rope, if we all work together. 22 00:01:10,000 --> 00:01:12,000 Let's talk a little bit about work. 23 00:01:12,000 --> 00:01:15,000 First, you have to have a force, a push or a pull. 24 00:01:15,000 --> 00:01:17,000 The force alone is not enough. 25 00:01:17,000 --> 00:01:20,000 To do work, the force must be applied through a distance. 26 00:01:20,000 --> 00:01:23,000 Here, hold onto this anvil for me. 27 00:01:23,000 --> 00:01:25,000 Sure, but why? 28 00:01:26,000 --> 00:01:27,000 Why? 29 00:01:32,000 --> 00:01:33,000 Getting tired yet? 30 00:01:33,000 --> 00:01:34,000 You bet. 31 00:01:34,000 --> 00:01:38,000 Because you haven't moved the anvil, you haven't done any work. 32 00:01:38,000 --> 00:01:42,000 Doing work and getting tired are not necessarily the same thing. 33 00:01:42,000 --> 00:01:44,000 Can we put this thing down? 34 00:01:44,000 --> 00:01:45,000 Of course. 35 00:01:45,000 --> 00:01:49,000 Now with the slingshot, I did work when I pulled on the strap 36 00:01:49,000 --> 00:01:51,000 and moved it back about one meter. 37 00:01:51,000 --> 00:01:54,000 When I let go of the strap, the slingshot did work on the tomato 38 00:01:54,000 --> 00:01:56,000 because I pushed it forward and sped it up. 39 00:01:56,000 --> 00:01:58,000 I love the slap. 40 00:01:58,000 --> 00:02:00,000 Now with the 25-kilogram anvil, 41 00:02:00,000 --> 00:02:03,000 I had to supply a force of about 55 pounds, 42 00:02:03,000 --> 00:02:05,000 going against gravity as I picked it up. 43 00:02:05,000 --> 00:02:08,000 The higher I lifted the anvil, the more work I did 44 00:02:08,000 --> 00:02:11,000 and the more gravitational energy the anvil had. 45 00:02:11,000 --> 00:02:13,000 Then the anvil must have had a lot of energy 46 00:02:13,000 --> 00:02:15,000 because it sure crushed the cantaloupe. 47 00:02:15,000 --> 00:02:18,000 But Jacob is heavier than 55 pounds. 48 00:02:18,000 --> 00:02:20,000 Does that mean it would take more work to lift him? 49 00:02:20,000 --> 00:02:21,000 Yes, that's right. 50 00:02:21,000 --> 00:02:23,000 Since work is equal to force times distance, 51 00:02:23,000 --> 00:02:27,000 increasing either the force or the distance will require more work. 52 00:02:27,000 --> 00:02:29,000 You said it took energy to do work. 53 00:02:29,000 --> 00:02:32,000 So where did the energy come from to lift the anvil? 54 00:02:32,000 --> 00:02:35,000 The energy came from the corn flakes I had for breakfast this morning. 55 00:02:35,000 --> 00:02:37,000 Corn gets energy from the sun. 56 00:02:37,000 --> 00:02:40,000 It's going to take a lot of energy to lift Jacob into the treehouse. 57 00:02:40,000 --> 00:02:43,000 I think it's going to take all our energy to do the job. 58 00:02:43,000 --> 00:02:44,000 Thanks, Dr. D. 59 00:02:44,000 --> 00:02:45,000 You're welcome. 60 00:02:45,000 --> 00:02:46,000 Bye.