## Sunday, December 7, 2014

### unit summary

Unit summary 3
Newton’s 3rd Law
The law states that any action has an equal and opposite reaction. We did an interesting experiment in class with weighing scales. We hooked them together and pulled, no matter how much we pulled the weight on each scale was the same. The forces were equal and opposite. The opposite forces are called an action reaction pair. An action reaction pair is the relationship between the opposite forces. For example: the apple is on the table. The table is pushing up the apple and the apple is pushing down the table. The forces in the example are equal and opposite and are an action reaction pair. In this case the earth pulls the apple down and the apple pulls the earth up. The earth has an equal and opposite force to the table pushing up, but it is not an action reaction pair because the pair can only be between two objects each affecting the other.
Tug of War
The forces of an action reaction pair are always equal and opposite so they cancel each other out creating a net force of 0. The way to move is the differences in the forces produced. For example: to win a tug of war the greater force has to be produced by the legs and the ground. No matter how hard one pulls the rope they can never exert more force than the other person according to the 3rd law. So one must have greater force between the legs and the ground, the greater force on the ground will move the opponents forward helping you win the tug of war. The key is to remember that you can never pull harder than your opponents you must put more force on the ground than them.
Vectors
Vectors are lines with arrow heads that indicate the direction and amount of force placed on an object. The vectors can be in any direction and can be summed up to give the actual direction and amount of force. The vectors are drawn to scale so the larger they are the large amount of force they represent. Adding vectors that are parallel is simple as you add them and if they are in opposite directions subtract. If they are at a 90 degree angle then use the formula a^2+b^2=c^2. If you are adding vectors the have neither of these conditions then create parallel line and form a closed figure. Where the new parallel lines intersect is the direction and amount of force there.
Tides
The tides of the earth are low and high constantly alternating in 6 hour intervals. The tides occur because of the difference in force between the sides of the earth and the moon. The moon pulls on the water on the close side of the earth towards it and the far side is pushed from the moon. How is this possible? The moon creates a force on both sides of the earth the force on the near side is stronger than the force on the far side. At the same time the earth is pulling on both sides. The difference in net force on each side of the earth because of the force of the moon creates mirroring high and low tide on the sides of the earth. The difference in force is always opposite, meaning that the force on the far side of earth is pulling the tide away from the moon creating high tide. The strong high tides are called spring tides and the strong low tides are called neap tides.
Momentum

Momentum is equal to mass*velocity. The mass and velocity are both directly related to the momentum so if velocity increases the momentum increases and if the mass increases the momentum increases. The momentum of an object cannot be greater than the momentum of the object it is colliding with, the total momentum before the collision is the same as the total momentum after the collision. The change in momentum is called an impulse and impulse equals force*time. The force and the time are both directly proportional to the impulse, but the force is inversely proportional to the time. This means that increasing the time before something hit another object reduces the force thus reducing the damage.