For example, Gravity pulls book downward. Book pulls gravity upward. Notice the underlined words: with an equal and opposite relationship, there must be the same verb, opposite directions, and the same two objects.
If the relationship was: hand pushes apple up, gravity pushes apple down, apple pushes hand down. This would only be an action and reaction pair because of the 3 different objects that are used.
For an object to exert an equal and opposite force there must be only 2 objects exerting the force; just think of it as equal and opposite, one object and two object.
In this example, the horse and the buggy and the equal and opposite pair. However, with the ground, horse, and buggy this is an action and reaction example. As the horse pulls the buggy forward, the buggy pulls the horse backward with an equal and opposite force. What makes the horse go forward is the horse's friction on the ground. Because the buggy is on wheels it does not have friction. Thus, because the horse's force on the ground is greater than the buggy's force on the ground the horse will move forward.
When drawing this picture, you need to make sure of to very important things: (1) that the vector at the top is equal and opposite (2) that your arrows point in the direction the word says (backward = back arrow).
Also, in class we did tug of war with girls vs. guys, and surprisingly the girls won!!! How did they win? Well, we made the boys place really fluffy, slippery socks on their feet, then went to the slippery floor. While the boys had socks on, the girls had their feet on the ground. This is similar to the horse and buggy demonstration. The girls had more friction on the ground, thus they were able to pull the boys and have more force, since the guys had on socks and didn't have a support force with the ground (friction). Because of this, the girls won the tug of war!!
This video is an example of vectors and adding forces. It demonstrates how to make vectors and when you might use them.
The next subject we learned in this unit was gravity and tides. One of the most important things to know is that tides are not caused by the force difference between the moon and earth or sun and earth. Tides are caused by the difference felt on opposite sides of the earth.
Everything with mass attracts all other things with mass.
Because the sun has a larger mass, it has a greater force on the earth than the moon does. It's important to remember that force depends on two things: (1) mass of object (2) distance between objects
Thus, the inverse square law 1/d^2.
And the Gravitational Force Formula is F = G (m1m2 / d^2) N = which is how someones weight is calculated.
This explains why a persons weight decreases as they get farther away from the earth (ground), for example, on Mt. Everest a person's weight is lower than when they are standing on the beach.
The two different tides are spring tides and neap tides. Spring tides are when the lowest are at their lowest and the highs are at their highest (then normal). Neap tides are when the highs are at their lowest and the lows are at their highest.
The change in P (momentum) is the same regardless of how you are stopped.
P = mv
(change in) P = Pfinal - Pinitial
Impulse is the force upon something and how long force is applied -- force x time = force applied.
Impulse = Force x change in time
J = F x (change in) t
Thus Impulse and (change in) Momentum are equal. J = (change in) P.
So why do airbags keep us safe??
The car wil be going from moving to not moving ( P = mv) & (change in P = Pfinal - Pinitial)
Thus the P is the same
The impulse will be the same regardless of how you are stopped ( J = change in P)
Thus impulse is the same (J = F change in t)
An air bag increases the time of the impulse, thus the force is smaller.
When a car goes from moving to not moving there is a conservation of momentum. Say a car that weighs 2kg is going to the right at 3m/s and the second car that weighs 3kg is going to the left at 3m/s. After the collision, the cars are stuck together. What's the final momentum?
This is how you find it.
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