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.

Unit 3 Reflection

During this unit of physics we covered from newton’s third law to the law of conservation of momentum. I enjoyed this topic of physics since it was easy to comprehend and had may relations to the physical world. This unit also allowed me to explore new paths of physics such as gravitational forces and how they affect our tides. On the first day of this unit the class was prompted with the question: “In a crash, who exerts a larger force on the other: a car or a truck?” In order to solve this problem and justify your answer you must understand newton’s third law. Newton’s third law states that ever action has an equal and opposite reaction. Newton discovered that if a force is exerted from object A onto object B, than Object B would exert and equal and opposite force onto object A. Since we know this it is impossible for one object to exert a greater force on the other. Both the car and truck will exert an equal and opposite force onto each other. If this is true, then why will the smaller car usually move backwards when hit by a big truck? Similar to a horse and buggy the horse pulls the cart forward; while the cart pulls the horse backwards (this is called an action-reaction pair). The cart will eventually move since it exerts a greater force onto the ground than the wheels on the cart. The cart moves forward since the horse pushes ground backwards and ground pushes horse forwards. This is also how a tug of war team wins. The winning team wins the competition since they exert a greater force on the ground than the opposing team. During this unit we also learned about vectors. A vector is a mathematical term showing both direction and magnitude. We use vectors in physics when there are two forces that are not in the opposite or same direction as each other. Picture you paddling across a river. You paddling allows you to move across the river while the current pushes the boat down the stream. We can represent this with two vector arrows, one in the vertical and one in the horizontal direction. Since the boat is experiencing a downward force from the current, the boat will not travel straight across the river. This is depicted in the picture in my blog. While the boat is on a heading for position A it will actually reach position B due to the force of the current pushing the boat downwards. Our picture shows the horizontal and vertical vectors as dotted lines and the actual force vector as the red line. When solving for actual force we use the fundamental equation a2+b2=c2. Using vectors, why does a box slide down a ramp? A box has a force of weight also known as gravity acting on it. This force of gravity is demonstrated through line 1. This is the first line when solving this problem. Our next line will be equal in magnitude to line 1 but in the opposite direction. We use this line to create our third line known as the guide line. Our third line will be our guide line. This line will go above our second line and help us when creating our support force for the box situation. Once we have finished the guide line we draw a line that starts from the center of the box until it hits the guide line. This line is green and is known as the support force. We then draw our vectors since this is a free body diagram. The vector lines are shown in grey. We are then able to finish and draw the resulting vector which is the purple line. This diagram shows why a box will go down a ramp. Next we learned about gravitational forces and physics. Everything in the universe that has a mass also has a gravitational force. The larger the mass, the larger the gravitational force. This is why the planet earth rotates around the sun rather than the sun orbiting the earth. The formula we use to calculate the gravitational force is; Universal Gravitational Formula = G((Mass of first object + Mass of second object)/Distance between both objects squared) F=(G)((M1+M2)/d^2) Since the gravitational force is so weak we add G which is equal to 6.67 x 10-11 Nm2/Kg2. From the formula we can determine that mass is proportional to gravitational force and inversely squared proportional to distance. Tides are produced due to the difference in force on either side of the planet. Since the ocean surrounds the world. One side of the planet will experience a different gravitational force than the other. This is how tides are produced. The moon orbits around the earth causing 2 high tides and 2 low tides every day. We also experience spring and neap tides. A spring tide occurs when the moon and sun are on either side of the earth, this produces very high, high tides and low, low tides. A spring tide occurs when the moon is perpendicular to the sun. This causes higher low tides, and lower high tides. Other bodies of water don’t experience tides since they aren't big enough to experience a difference in force. Momentum is defined as inertia in motion. Momentum is defined as the product of the mass of an object and its velocity. The equation for momentum is; Momentum= mass x velocity P= mv You may be wondering if a skateboard can have a larger momentum than an aircraft carrier. At first I thought that the answer was obvious but soon found myself wrong. A skateboard although small in mass can have a positive velocity. If the aircraft carrier is at rest than it doesn't have a velocity and therefore no momentum. Astonishingly, this means the skateboard has a larger momentum than the aircraft carrier. From momentum we get impulse. Impulse is force multiplied by the time the force is applied. The equation is as follows; J=F∆T We can use this equation when understanding how an airbag protects us from being hurt. When in a car accident the airbag will deploy. This occurs to reduce injury from the collision. The car goes from moving to not moving during the collision. The change in momentum is the same if we hit the airbag or the dashboard. If change in momentum is the same, than impulse (J) is also the same whether you hit the airbag or the dash board since J is the same (∆P=J). Airbags will therefore increase the time and decrease the resulting force. We can represent the difference between the airbag and the dashboard through the equations below: J = F∆T - Airbag J = F∆T – Dashboard The law of conservation of energy states that energy can neither be created nor destroyed, only transformed. Due to this law, any energy in a system will never diminish, only transfer. If a small car hits another small car at rest and they stick, then both the cars will move with a slower velocity however the momentum will be conserved since there is a greater mass. The law of conservation of momentum can be depicted as; ∆P = PFinal – PInitlal FA = -FB

FA∆T= -FB∆T Thank you for reading my blog and I hope you found it useful and enjoyable!

Tides in Bermuda

You may be wondering how tides happen in our world? Before we answer that question we must know that there are four different tides every day. There are two high tides and two low tides every single day. This happens because of the gravitational pull of the moon. The moon is pulling the earth equal and opposite to the gravitational force. Different tides occur throughout the day since the moon rotates around our planet. Think of a tug of war between the moon and the earth. Tides occur because of the gravitational force of the moon. In the photo bellow it is interesting to notice that the seaweed is higher than the water line. The seaweed is so far up the beach because the high tide pushed it there. That means there is a low tide currently. A really high tide will occur during a full moon and a very low tide will occur during a new moon. To answer our initial questions tides are caused by the difference between the forces on each side of the earth.