Saturday, February 21, 2015
Unit 5
Work is force times distance (work=fxd). It can only occur when parallel, like a person picking up a cat up off the ground. If the person walked forward while holding the cat, work would not occur. Work is measured in joules.
Power is work divided by time (power=work/time). Power is measured in watts and unlike work, which is required for power, requires time.
Work is related to Kinetic energy because work= a change in kinetic energy. A change in kinetic energy = KEfinal-KEintitial. Kinetic energy = 1/2 m v ^2.
There are three types of simple machines: ramps, levers, and pulleys. A simple machine decreases the amount of force needed by increasing the distance covered. For example, someone could pick a very heavy cat up off the ground, or they could push it up the ramp. Picking it straight up would require a large amount of force, but a short distance, but pushing it up the ramp would require much less force because it would be a longer distance.
This happens because of conservation of energy. This means that the work in has to equal the work out. In the case of machines this trade of distance and force looks like this: fD=Fd. This concept can also be applied to a pendulum or a roller coaster. As far as a pendulum is pulled to one side, it will never get higher than that and a roller coasters hills can never be greater than the first one.
This is because of potential and kinetic energy. Potential energy = mass x gravity x height. PE does not require motion, just height. When something is at the top of a fall, it has a certain amount of PE and no KE and at the very end of a fall it has no PE and a certain amount of KE.
Monday, February 2, 2015
Unit 4
Rotational speed is the number of rotations per amount of time. If a lady bug was sitting any where on an LP, it would always have a rotational speed of 33 1/3 rpm.
Tangential speed depends on the radial distance, or the distance from the axis of rotation.
Real life applications of these concepts can be seen in train wheels and gears. Gears work by moving at the same tangential velocity and different rotational velocity. Train wheels self correct by having the same rotational velocity but different tangential velocity.
Rotational inertia is how resistant something is to rotation and it involves the distance from the axis of rotation. If there is a meter stick with two weights taped very near the middle, it would rotate easier because it would have a short distance to the axis of rotation and therefore a lower rotational inertia. If there is a meter stick with two weights taped towards the end, it would be more difficult to rotate because it would have a long distance to the axis of rotation and therefore a higher rotational inertia.
Conservation of angular momentum means that the torques are equal in a situation such as a figure skater extending their arms and then curling up. When a figure skater is extended, she moves much slower than she does when curled up. Despite this, the angular momentum is the same before and after because when extended, the skater has a small rotational velocity and a large rotational inertia and when curled up, the skater has a large rotational velocity and a small rotational inertia.
Torque causes rotation. Torque = force x lever arm (distance from the axis of rotation). A large force, a large force, or both, create a large torque. For instance, if someone was having a hard time using a wrench, they should get a longer wrench because it would increase the lever arm and therefore create more of a rotation. When something is balanced, its clockwise and counter clockwise torques are equal.
The center of gravity is the average location of mass in an object. The base of support is like the bottom of a box or someone's feet. When the center of gravity is above the base of support, there is no torque/rotation. Lovering the center of gravity makes it more difficult to rotate the center of gravity outside of the base of support. Making the base of support lower creates more stability as well.
Centripetal force is an inward seeking force. For instance the moon stays in orbit around the earth because of the centripetal force pulling it to earth and the fact that it wants to keep going straight.
Tangential speed depends on the radial distance, or the distance from the axis of rotation.
Real life applications of these concepts can be seen in train wheels and gears. Gears work by moving at the same tangential velocity and different rotational velocity. Train wheels self correct by having the same rotational velocity but different tangential velocity.
Rotational inertia is how resistant something is to rotation and it involves the distance from the axis of rotation. If there is a meter stick with two weights taped very near the middle, it would rotate easier because it would have a short distance to the axis of rotation and therefore a lower rotational inertia. If there is a meter stick with two weights taped towards the end, it would be more difficult to rotate because it would have a long distance to the axis of rotation and therefore a higher rotational inertia.
Conservation of angular momentum means that the torques are equal in a situation such as a figure skater extending their arms and then curling up. When a figure skater is extended, she moves much slower than she does when curled up. Despite this, the angular momentum is the same before and after because when extended, the skater has a small rotational velocity and a large rotational inertia and when curled up, the skater has a large rotational velocity and a small rotational inertia.
Torque causes rotation. Torque = force x lever arm (distance from the axis of rotation). A large force, a large force, or both, create a large torque. For instance, if someone was having a hard time using a wrench, they should get a longer wrench because it would increase the lever arm and therefore create more of a rotation. When something is balanced, its clockwise and counter clockwise torques are equal.
The center of gravity is the average location of mass in an object. The base of support is like the bottom of a box or someone's feet. When the center of gravity is above the base of support, there is no torque/rotation. Lovering the center of gravity makes it more difficult to rotate the center of gravity outside of the base of support. Making the base of support lower creates more stability as well.
Centripetal force is an inward seeking force. For instance the moon stays in orbit around the earth because of the centripetal force pulling it to earth and the fact that it wants to keep going straight.
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