What is rotational Inertia?
-The property of an object which resists changes in motion
-It depends on: mass (more mass=harder to spin) (less mass= easier to spin)
Rotational velocity?
-How fast you rotate
Why do runners bend their legs instead of keeping them straight?
-Because when they bend their knees, they are bringing them closer to the axis of rotation. The closer to the axis of rotation the less inertia and the easier it is to move.
The skater is experiencing the same thing:
In the first picture her mass is spread out far from her axis of rotation so she will have more rotational inertia so she will not go as fast.
In the second picture her mass is brought towards the center, so she will have less inertia thus making her rotational velocity increase.
What is tangential velocity?
-The linear speed of something moving along a circular path
How does a train's wheels stay on the track?
In this picture the inside part of the wheel to the left has a higher tangential velocity than the one to the right because it is larger and covering more distance.
Since the tangential is higher on the inside of one wheel, it causes the train to tilt inward and self correct.
Who has a higher tangential velocity on a carousel? Rotational?
-The person furthest from the center has the greatest tangential velocity
- They have the same rotational because the go around the same amount but the person on the outside is covering more distance than the person on the inside so they have a higher tangential velocity.
In these gears how does the Tangential and Rotational velocities compare?
The smaller gear in this photo will rotate twice while the bigger one rotates once which means they have different rotational velocities. They have the exact same tangential velocity though because they cover the same amount of distance in the same amount of time.
How does Inertia apply when you are rounding a curve in a car and you push up against the car door?
-Since you are still moving forward when the car is turning, the door is the object that stops you from moving in that direction and causes you to move in the direction of the car again
Conservation of Angular Momentum
How do you find the angular momentum?
-angular momentum before = angular momentum after
-angular momentum = rotational inertia X rotational velocity
What does angular momentum rely on?
-rotational inertia
- rotational velocity
When someone is running and they bend their knee, what happens to their mass as they bend their knee?
-their mass is lowered and so is their center of gravity which stays within the base of support
Torque
What is torque?
-it causes rotation
-torque= force X lever arm
-the larger the force to greater the torque
-the larger the lever arm the greater the torque
What is the lever arm?
-the distance from the axis of rotation
For example:
For example:
In this picture more force is required to push the door when you are pushing towards the hinges.
Less force is required when you push the door further from the hinges because the lever arm is larger.
*BIG TORQUE = BIG ROTATION*
If you attached a rope to the end of a wrench would that increase the torque? Why or why not?
-no because the lever arm actually isn't longer since you are unable to apply a large force on it. You would need to use something stronger like a pipe.
Where is the best place to put a door stop: in the middle of the door or the edge?
-towards the edge because it would require less force than the middle of the door since the lever arm is longer
Center of mass/ gravity
What is the center of mass?
-An object's average position of all of the mass
How does an object balance?
-If the center of mass stays within the object's base of support
Why do you bend your knees in sports?
-gives us a big support base
-makes it so that your center of gravity lowers and remains within the base of support
Why is it more beneficial for a tight rope walker to hold a pole that droops?
-because it lowers the center of gravity so you won't have a torque
-so that you can distribute your mass-->balance
Why is it better to hold two buckets rather than one?
-so that the mass is distributed which creates balance
If you draw a picture and draw a straight line coming from the center of gravity down and it stays within the base of support it means it will not fall over. If you draw a different picture and the box is tilting and the center of gravity is outside of the base of support it will fall over. (sorry I can't draw a picture-tech difficulties)
Centripetal and Centrifugal force
What is centripetal force?
-a force that is center seeking
-for example if you are driving around a curve the centripetal force is what causes the car to curve
What happens in a washing machine?
This unit went pretty well for me. I enjoyed the concepts that we learned and I overall did well on my quizzes. My quiz grades was something that I wanted to improve and I think that I reached this goal. It took me a little while to fully understand rotational and tangential velocity but once I really sat down and really wrestled with it I finally got it. Next unit I want to focus again on my quiz grades, and I think that if I am able to do well on my quizzes I will do well on my test. Overall I really enjoyed this unit and the labs that we did. I think it went smoothly because I really tried to stay focused in class.
Less force is required when you push the door further from the hinges because the lever arm is larger.
*BIG TORQUE = BIG ROTATION*
If you attached a rope to the end of a wrench would that increase the torque? Why or why not?
-no because the lever arm actually isn't longer since you are unable to apply a large force on it. You would need to use something stronger like a pipe.
Where is the best place to put a door stop: in the middle of the door or the edge?
-towards the edge because it would require less force than the middle of the door since the lever arm is longer
Center of mass/ gravity
What is the center of mass?
-An object's average position of all of the mass
How does an object balance?
-If the center of mass stays within the object's base of support
Why do you bend your knees in sports?
-gives us a big support base
-makes it so that your center of gravity lowers and remains within the base of support
Why is it more beneficial for a tight rope walker to hold a pole that droops?
-because it lowers the center of gravity so you won't have a torque
-so that you can distribute your mass-->balance
Why is it better to hold two buckets rather than one?
-so that the mass is distributed which creates balance
If you draw a picture and draw a straight line coming from the center of gravity down and it stays within the base of support it means it will not fall over. If you draw a different picture and the box is tilting and the center of gravity is outside of the base of support it will fall over. (sorry I can't draw a picture-tech difficulties)
Centripetal and Centrifugal force
What is centripetal force?
-a force that is center seeking
-for example if you are driving around a curve the centripetal force is what causes the car to curve
What happens in a washing machine?
The water is in motion so it will continue to stay in motion unless acted upon by an outside force and in this case the centripetal force is not acting on it so it will continue moving.
CENTRIFUGAL FORCE IS NON EXISTANT
But some say that centrifugal force is what pushes you against your car door when you are rounding a corner. This is not true. What is happening is due to inertia. An object in motion tends to stay in motion unless acted upon by an outside force. In this case your body is still moving forward and the car door is the object that stops you and makes you move in the direction the car is going again.
This was a pretty thorough wrap up of unit 4. I liked how you used a sort of note-like bullet point format- this made the post easy to read and even though it was long and covered a lot of information, it was not intimidating with big paragraphs. Also I think this will probably make it easy for you to reread and study the information later for the final exam in May. This was different from my post because I usually use paragraphs and have large chunks of text but that is probably not the easiest or most interesting to read. Similar to my post, you used a lot of pictures. I thought the ice skater and the torque pictures were the best ones- they really clearly demonstrated what you were explaining. The only constructive criticism that I have is to check for typos but that's it- great job!
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