Unit 5 Picture

This picture demonstrates a balanced object. The meter stick is placed on the edge of a table with a 100g weight on the end. If you wanted to find the weight of this meter stick you can calculate the torque on one side of the meter stick and then find the force of the meter stick. Torque is the tendency for an object to rotate. Since the meter stick is perfectly balanced we can say that the torque on each side is equal. 

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.

Mass of a Meterstick

During physics class we were instructed to determine the mass of a meter stick by using a meter stick and a weight. In order to fully comprehend the objective of this project it is important to identify where the center of gravity is located. In order to find this point balance the meter-stick without the weight first. For many meter sticks the center of gravity is located close to 50cm. Once you have determined the exact point where the meter-stick can balance you then place the weight on one end of the meter-stick and make it balance balance. For me this point was located at 30cm. We now have to identify that when 100 grams is added to the end of the meter stick, it will balance at 30cm. Torque is the tendency of an object to rotate around the axis of rotation. This can be calculated by multiplying the lever arm and the force on the object. Torque = lever arm x force When the object balances the torque on each side of the object is the same. We now know hat the lever arm of the meter-stick is 30cm but we need to determine the force acting on the meter stick. The 100 gram mass is our force since gravity is acting on the mass. We can convert this mass to weight (a force) by multiplying the mass by gravity (9.8 N/kg). Since gravity is in kg we first must convert the grams into kg which is .98 kg. Now that we have determined our lever arm is 30cm and our force is .98 N/kg we can determine the toque on one side of the meter-stick thus allowing us to find the total mass of the meter-stick. Once my group made this calculation we discovered that the torque on the system is 29.4. Once we found the torque, we determined that since the lever arm was 30 cm we had to subtract this amount by the entire lever arm when no weight is added to the system. Since the system in in equilibrium at 50cm, we subtracted the 30cm by 50cm. 20cm is our new lever arms and is vital when deriving the mass of the meter stick. Since we know the total torque we can reorganize the equation in order to find the mass. This equation would be; Torque/Lever arm= Force Once we calculated that the force equated to 1.47 we needed to convert this number to grams. We were able to do this by dividing this value by 9.8 (the force of gravity) and then multiplying by 100. This equated to the value of 150g. Once we weighted the meter stick, my group discovered that the actual weight of the meter stick was 150.4 grams. Since our estimation was off by only 0.4 grams my group was amazed and in shock. The picture below will show you how to set up the experiment. I have indicated that 30cm is where our meter stick balanced however this is different for every meter stick.

Introduction to Torque

This video was very useful when understanding Torque. The video talks about center of gravity and gives demonstrations on torque. The video also defines Torque and provides the universal symbol. The video explains directions of torques and when to determine torque values as positive and negative. He also demonstrates an example when the net toque of an object is zero and how to determine the torque.

Merry-Go-Round

Now, although this looks a little fun it is a very bad idea. They used a motorcycle to increase the speed of the merry go round. Although they went very fast can you identify something that reduced their speed? Since the two individuals were sitting at the end of the wheel, the wheel had a higher rotational inertia and thus had a lower rotational velocity then if they moved to the middle. The two individuals lowered the rotational velocity as much as they could since they were located faraway from the axis of rotation.