What we discussed in this unit was centered around the concept of Torque.
What is Torque?
Torque is combination of force and the lever arm applying that force that causes rotation.
The equation for Torque is Torque = (Force)(Lever arm)
The units used for torque are NM (Newtons meters)
The lever arm is the distance from the object that is being pushed upon.
An example of Torque is when someone tries to turn a bolt with a wrench. If that person can't get the bolt loose he could either find someone stronger to apply more force or get a bigger wrench to increase the lever arm, or he could do a combination of both.
Another Concept we explored was the center of mass/ gravity.
The center of mass is the mean position of all an objects mass where gravity is principally acting upon.
If the center of is inside an area called the base of support then the object with not fall ( due to gravity)
THe base of support is the area where the most of the weight of a body is supported by
Is these two dominos the red circles are there centers of mass. the first one is safely positioned above the base of support (the red arrows point to it). The second one has is CM outside of the base of support and so is producing a Torque.
Why do athletes widen there feet ?
This increases their base of support so it's harder for them to get knocked down.
How do Ice skaters move faster when they bring there arms in
Why do Ice skaters spin faster when they bring in there arms?
This is due to a concept called rotational inertia, which means that once an object remains rotating it will want to keep rotating (like the Earth!). The farther away an objects mass is from the center of gravity the harder it will to make it move. As the ice skater brings in his arms he brings all his mass closer to his center of gravity, thus making him go faster.
Angular momentum is the momentum at which the skater is rotating. Two things create determine the position of angular momentum.
1. Rotational Inertia
2. Rotational Velocity
So the equation will look like this
Angular Momentum = Rotational inertia times Rotational Velocity
And because momentum is conserved angular momentum before = angular momentum after
which could also be displayed as.
Rotational inertia times rotational velocity = Rotational inertia times rotational velocity.
Now lets complicate things by adding Torque and the Center of Mass into one problem
The meter stick pictured above is on it's center of mass (where the fulcrum is positioned). Lets say that one side of the the stick has a heavier weight attached to it. how are we going to make the meter stick balanced again. Now the fulcrum has split both sides of the meter stick into two halves. Both sides could cause a torque depending on which one is bigger. But in order the the stick to be balanced the counter clockwise torque must equal the clockwise torque. In an equation it would look like torque = force times lever arm equals torque = force times lever arm. So if one side of the meter stick has a bigger weight (i.e. force) then the other side would need to have a longer lever arm for the meter stick to be balanced.
Now lets take a look at rotation.
There are two velocities that act on rotating object.
Tangential velocity is the first. T velocity concerns the speed of a rotating object like how fast it is moving.
If we take a look at the picture above we can see that the figures are actually moving faster the farther they get away from the center of the circle and that the center figure is merely rotating. Why is this? lets take a look at the other type of velocity to answer that question.
Rotational Velocity is how many times an object circles back to the point at which is started rotating.
If we take a look at the two gears above we can see that one is larger than the other. The smaller one has a larger rotational velocity because it takes less time to circle around to it's starting position while the big one has a smaller rotational velocity because it takes longer to circle around to the same point at which it started at.
Of course if the bigger gear wanted to keep rotating at the same speed as the smaller one it would need to increase it's speed (or it's Tangential velocity) so that it could rotate more.
While we're on the topic of rotating lets talk about the concept of centripetal force
Centripetal force is center seeking force that causes an object to turn.
As seen in the picture above the centripetal force is represented by the center blue arrow, this force is what causes something like a car to turn in another direction. The green arrow represents the cars velocity as it attempts to keep going the same direction. Although if neither of the forces are stronger than each other than the car will turn in between both arrows in the direction of the black arrow.
Have you ever been sitting in a car while it's turning and felt like you ran into the side door. Well that due to something that we call centrifugal force. Though this is not a force at all is is merely the product you going forward while some centripetal force is being applied and you wanting to stay forward. that car door is actually pushing on you causing you to turn.
Centrifugal force is also the reason why clothes get dry in the drying machine. The cylinder that your clothes are put into hold then in but because there are hole in it some water is not forced to stay in while the machine is spinning. So the water simply keeps going in the same direction right through those holes and out of your clothes.
What was difficult.
THe ONQ's were really hard. I often missed little details or even large concepts that cost me points. I did much better on the regular quizzes because I understood what I got wrong on the ONQ's. I haven't really overcome this but my regular quiz scores have jumped since last semester. I'll try to take better notes ( i.e. make them clearer) so that I could do better on the ope note quizzes. I'll also try to pay attention to more of the details in the videos.
Real World Problem.
What if I took a fan and used it to blow over a cup sitting on a table. Now if I move that fan farther back it would be harder to blow over the cup, but when I moved the fan away from the cup am I not increasing the lever arm? Wouldn't it be easier for me to knock the cup down?
