Unit 5 Reflection Blog

During this unit we learned about Rotational motion, Rotational Inertia, Rotational velocity, angular momentum, torque,and centripetal force. This unit was more technical than previous units and proved more difficult to grasp and comprehend. Our introduction to Rotational Motion was difficult to understand. After preforming a demo outside it was easier to understand. We were presented with a question that confused most of the class. If two people are on a merry-go-round, one close to the middle and one far from the middle, who has the greater velocity? Initially, I thought that everyone in the merry-go-round would move at the same speed. During the demonstration the teacher stood in the middle and half the class stood in a line next to the teacher and the other half of the class stood on the other side. We were all told to keep in line with the teacher as we rotate in a circle. Being at the end of the line it proved to be very difficult to keep up with the rotating circle. It then became apparent that although our rotational velocity was the same, we all had a different tangential velocity. Rotational velocity is the amount of rotations in a given time period. Tangential velocity is the rotational velocity of an object over a period of time. The further an object is from the axis of rotation the higher the tangential velocity. When discussing rotational velocity we can use gears. In the picture provided you will notice two gears, one small, and one large. Although they are both rotating with the same velocity the smaller gear is completing one rotation faster than the larger gear. This means that the small gear has a larger rotational velocity than the bigger gear. We apply the idea of gears in many products such as bicycles, and cars.

During this unit we also discussed the implications of putting larger wheels on you car and how it relates to physics. If you put larger wheels on your car without changing the speedometer you may get a ticket. This occurs because the speedometer is programmed to measure rotations per minute and translate it into speed. If you have bigger wheels the speedometer will read a lower speed then when you are actually going. the wheels cover a larger distance in one rotation. With big wheel, one rotation will be a further distance.

Rotational inertia is how much an object is willing to spin. This is the property of an object to resist the change in spin. Rotational inertia depends on where the mass is located. Angular momentum is determined by two factors: rotational inertia  and rotational velocity. Since we know the law of conservation of momentum, we know that the angular momentum before is equal to the angular momentum after. We can control our rotational inertia which directly influences our rotational velocity. An example of this is an ice skater. The ice skater will brim their arms in. close to their axis of rotation to increase there rotational velocity  If the ice skater wishes to slow down they will extend there arms, increasing their rotational inertia and decreasing their rotational velocity.

We also learned torque. Torque is the tendency of an object to rotate around its axis of rotation. The more torque an object has the more likely that object is to rotate. Torque is calculated by multiplying the force applied by the lever arm. An example of torque in the real world is a wrench loosening a bolt. The larger the wrench the larger the lever arm. It is important to remember that torque is a perpendicular force. If an object is balanced it is said to have an equal torque on each side. There is always a counter clockwise torque and a clockwise torque. If the object rotates clockwise, the it has a clockwise torque, if it rotates counter-clockwise, it has a counter clock wise torque. When learning this we were told to predict the mass of a meter stick only using a 100g weight. This demonstration was very difficult since we had to calculate the toque of the meter stick balanced with the 100g weight on it. We then had to determine where the center of gravity for the object is. We learned that the center of gravity for any object is underneath that objects base. This point is where all the mass is also located.

Centripetal force is a center seeking force. Centrifugal force, although not real, is a fleeing force. An example of this force in our everyday life is when a cyclist turns and dosent fall. This occurs because the cyclists support force and force of weight causes him to move towards the center of the circle.