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!