Unit 4 Picture

This picture is an example of centripetal force. The swings on this ride are connected to the center consul which keep them towards the center. This picture is real life example of the flying pig demonstration we did in class. If one of the swigs were to come off, that swing would fly in a straight line that is tangent to the path it was previously traveling. 

Unit 4 Reflection

Unit Reflection:

In unit 4 we learned about torque, rotational and tangential speed, rotational inertia, center of mass, center of gravity, centripetal force, and centrifugal force. To start this section we learned about rotational speed, which is the number of revolutions that are made in a certain amount of time, and tangential speed, which is the distance covered in a certain amount of time. We learned that while two people on a merry go round may have different tangential speeds, they would both have the same rotational speed. We applied our knowledge of tangential speed to roller derby and discovered that the purpose of “the whip” move is so that the skater being whipped could gain a greater tangential speed and therefore pass her opponents. Similarly we leaned that if you increase the size of your tires on your car you could be driving at a faster speed than your speedometer reads. An objects angular momentum has to do with how much mass is closer or further form the axis of rotation. An object with a larger amount of mass away from the axis of rotation is going to move slower than if the mass was closer to the axis of rotation. An object with more mass further away from the center is going to have a greater rotational inertia because it is going to be more difficult for the object to begin to move. If the mass were more towards the center however, the object is going to have a lower rotational inertia and be easier to begin moving. Next we learned about torque and center of mass. Torque causes rotation. Torque = lever arm X force. The longer the lever arm that you are using to turn an object the smaller force you are required to apply and vice versa. We then learned that because of center of mass, when we put on our backpacks, we subliminally lean foreword so we don’t fall. Because we increase our mass behind our natural center of mass we need to lean foreword and balance out our new center of mass. This action keeps us form falling over. As long as our center of mass remains under us we will stay standing. We also learned that the leaning tower of Pisa does not fall over because its center of gravity is being supported by it’s base. In other words the center of gravity is within the base of support. We then moved on to centripetal and centrifugal forces. Centripetal force is the center seeking force when you are turning on a curve in your car. The feeling of fling that you feel when you are turning on this curve is the centrifugal force. The center fleeing force you feel is the fictitious force. We learned that during the spin cycle when your clothes are in the washing machine, the water leaves the basin through little holes not because of a force but because of a lack of force present. Personally, I struggled with this unit more than I have with the others. Coming and asking questions in the morning would have been beneficial. 

Center of Mass Resource

http://www.youtube.com/watch?v=DY3LYQv22qY

In this video, people throwing objects demonstrate center of mass. When the objects are thrown in the light they seem to be moving all over the place, but when the lights are turned off and the center of mass is painted it looks as though the object is moving through the air smoothly. With the lights off you can clearly see the center of mass, whereas when the light are on it is more difficult to see. 

Angular Momentum Resource

This video clearly demonstrates angular momentum. You can see how when the mass is closer to the axis of rotation of the object the speed at which it spins increase. This is similar to an ice skater, gymnast, or a diver. In order to spin quickly all three of these sports require the athlete to pull all of their mass in towards the axis of rotation. 

Unit 3 Blog Reflection

This unit we learned a lot of new material. We started the unit off learning about vectors and calculating what direction an object is going to travel in if it has two different forces acting on it. We learned that you would dray two lines that represent the two different forces and one line that bisects your starting two lines that represents what direction the object is going to move in. With our new knowledge of vectors we learned the physics relating to why a box on a ramp slides down the ramp. After vectors we moved onto the universal gravitational force which is F=G(M1)(M2)÷d². This formula can be used to find out the weight of someone or something. The force that you have on the surface of the Earth is different then the force that you are going to have on a large mountain. This is because force is inversely proportional to distance. If the distance is further rather then shorter then the force is going to be lesser. If the distance is going to be shorter rather then shorter then the distance is going to be greater. On the other hand, force is directly proportional to mass, the greater the mass the greater the amount of force, the smaller the mass is the lesser the amount of force. Next we talked about tides. Tides are caused because of the difference in force felt by opposite sides of the Earth. The two opposite sides of the Earth, although they are experiencing different forces, are experiencing the same tides. When the moon is in a new or full state spring tides occur. During spring tides the highs are higher then normal and the lows are lower then normal. On the contrary, when the moon is waxing or waning, the lows and highs are regular. After tides we moved on to momentum. Momentum is inertia I motion. Momentum = massXvelocity. (p=mv) Along with momentum we learned about impulse. Impluse is represented with the letter j. J=the change in p and J = f∆t. The impulse is the same regardless of the amounts of force and time. The only difference is with the amount of time and the amount of force. The longer it takes for the change in momentum or impulse to complete the lesser the force is going to be. The shorter it takes for the impulse to complete the greater the amount the force is going to be. This is why gymnasts use mats. The mats extend the time of impulse so the force exerted on their feet is less. Without the mats the time of impulse is going to be smaller and the force on the gymnasts feet is going to be larger, because of the greater force the gymnasts risk injury. Next we worked with colliding objects. When one object is moving and runs into another object and then forces that one to move or when two objects are moving toward each other we used the formula M_AV_A-M_BV_B=(M_A+M_B)V_AB. Using this formula we are able to solve for V_AB which will tell us the velocity that the whole system is moving with after the collision. We then asked how it was possible for a ball that is moving with a horizontal velocity to hit a ball that is still and cause it to move in the vertical direction. This is possible because the forces are equal and opposite, so the vertical forces created are going to add up and equal to zero!  

Unit 3 Picture

This picture is an example of tides. Tides are caused because of the difference in force felt by opposite sides of the Earth. The tides that come in and out of this rocky area are going to occur every six hours. If this were a low tide right now, in six hours there would be a high tide and six hours after that would be low tide again. If this was a low tide, then the opposite side of the Earth is also going to be experiencing low tides, the same goes for high tides. If the moon were a full moon or a new moon, the high and low tides would be more dramatic. These are called spring tides. The less dramatic tides that occur during waxing and waning moons are called neap tides.

Tides Resource

This video clearly shows a change in the tides as the day goes on. In this video it starts out with people on the beach area, but as the day goes on the people are being pushed back by the rising tide until the water is completely covering the beach area. You later see kayakers who come and boat around the now fully watered area. This video demonstrates how a tide starts out low and works its way back to a low tide at the end of the day which is approximately twelve hours.