00:01
This video i'm just going to give you a quick example of how to draw a free body diagram.
00:05
Okay, so our system is we have a mass, some mass m on a string, and we're going to start it spinning in a circle in the horizontal plane here.
00:19
So this was our original string.
00:22
Then we started spinning.
00:23
The mass is now traveling around in this circle.
00:27
And that's going to stay in one horizontal plane so it's y value is not going to change it'll be at the same height the whole time and we want to look at all the forces acting on this object of mass m and then we want to draw a free body diagram for it so let's look at the vertical direction first what forces do we have acting we have some tension force from the string here and we have the gravitational force due to the object's weight.
00:58
And we've already said that this object is not moving at all in the vertical direction.
01:04
So we know the sum of the forces acting on it must be zero because its acceleration is zero.
01:09
That follows directly from newton's second law.
01:11
Sum of forces acting on an object equals its mass times its acceleration.
01:16
So in the y direction, we have tension in the positive direction minus gravity in the negative direction equals 0.
01:26
Right, and we can find the tension here.
01:31
Say we're swinging the ball in a circle with some angle to the vertical theta.
01:37
All right, so the y component of this is just cosine theta, so t cosine theta equals m g.
01:51
And we can see that simply equals to t sign of whatever this angle is that we're swinging at, and that's going to equal mass times acceleration in the x direction...