(II) Three children are trying to balance on a seesaw, which...

Name: Problem 17, Chapter 9: Physics: Principles with Applications
Uploaded: 2019-09-05T14:11:49-08:00
Duration: 5 min 11 s
Channel: Kebur Fantahun
Description: (II) Three children are trying to balance on a seesaw, which includes a fulcrum rock acting as a pivot at the center, and a very light board 3.2 m long (Fig. 9-57). Two playmates are already on either end. Boy A has a mass of 45 kg, and boy B a mass of 35 kg. Where should girl C, whose mass is 25 kg, place herself so as to balance the seesaw? FIGURE 9–57 Problem 17. (Figure can't copy)

(II) Three children are trying to balance on a seesaw, which includes a fulcrum rock acting as a pivot at the center, and a very light board 3.2 m long (Fig. 9-57). Two playmates are already on either end. Boy A has a mass of 45 kg, and boy B a mass of 35 kg. Where should girl C, whose mass is 25 kg, place herself so as to balance the seesaw? FIGURE 9–57 Problem 17. (Figure can't copy)

Key Concepts

Torque

Torque, also known as moment, is the measure of the tendency of a force to rotate an object about a pivot point. It is calculated by multiplying the force applied (often related to weight in balancing problems) by the distance (lever arm) from the pivot. Understanding torque is essential when determining how forces cause rotational motion or balance in a system.

Lever Arm

The lever arm is the perpendicular distance from the pivot point to the line of action of the force. This concept is crucial because the effectiveness of a force in producing rotational motion depends directly on this distance. A force applied at a longer lever arm produces a greater torque, which is fundamental to solving balance challenges.

Static Equilibrium

Static equilibrium occurs when all forces and torques acting on a system are balanced, resulting in no net motion. In problems involving seesaws or levers, achieving static equilibrium means that the sum of the torques acting clockwise about the pivot equals the sum of the torques acting counterclockwise, thereby keeping the system balanced.

Transcript

00:01 Chapter 9, problem 17.

00:04 Three children are trying to balance on a seesaw, which includes a fulcrum rock acting as a pivot at the center, and a very light board 3 .2 meters long, figure 9 .57.

00:14 Two playmates are already on either end.

00:18 Boy a has a mass of 45 kilograms, and boy b, a mass of 35 kilograms.

00:25 Where should girl c, whose mass is 25 kilograms, place herself so as to balance the seesaw? so my favorite type of questions, balancing questions, because we already know ahead of time what we need to look for.

00:40 Most of the time, that's going to be summing the torques is going to be equal to zero or summing the forces is zero.

00:45 And we have what we call equilibrium or balance.

00:51 And so it's a very important point to say first that girl c should be placed where the sum of the torques will be zero.

00:58 That's one.

01:00 Well, not where the sum of the torques will be zero.

01:03 I shouldn't say.

01:06 She should be placed such that when you sum the torques, it will be zero.

01:11 Not exactly where it's zero.

01:15 Sorry for that confusion.

01:16 We know that the left side is heavier.

01:19 So if we can just imagine the children, there's our 45 kilogram boy on the left, 35 on the right.

01:25 So we, just from that, we know that it's going to be, we know the seesaw is going to be tilted a little bit more towards the left.

01:33 So we already know we want to put it.

01:34 We want to put the trial on the right side, put girl c on the right side, but we just don't know the distance.

01:41 In cases like this, we are given a lot of information in the problem, so we should be able to find out what that distance is based off of all the other factors, including the mass and the length of the board and all these things.

01:58 But i think at this point, the board is very light, so i don't think we consider the mass, the center of mass of the board.

02:03 Let's see.

02:15 Like i said before, these are very key words, balanced or equilibrium.

02:20 This just means that you want the sum of your torques to be zero.

02:25 And here we have a picture, a free body diagram of our situation, right? so child a is sitting on the left.

02:34 It is going to feel a weight downwards.

02:37 Same for b and c.

02:38 But they're both on the right, of course, because a was heavier than b...