1. Newton's 3rd Law and Action-Reaction Pairs
2. Horse and Buggy/ Tug O' War
3. Nonparallel Forces
4. Gravity and Tides
5. Momentum and Impulse Relationship
6. Conservation of Momentum
Newton's 3rd Law
Newton's 3rd Law states that every action has an equal and opposite reaction. When talking about this law in action, we use the term action-reaction pairs. Below is an example.
In the picture above, earth PULLS the book DOWN, the book PULLS the earth UP.
Three things you should remember when writing a action-reaction pair:
1. The verb stays the same
2. The directions switch
3. The objects stay the same but trade places
Parallel Forces: Horse and Buggy Problem
Something that goes hand in hand with Newton's 3rd Law, action-reaction pairs are composed of parallel forces. One of the examples we stressed the most during this unit was the horse and buggy problem, which I will show and explain below.
The horse and buggy pull each other an equal and opposite amount. So, how does the horse pull the buggy? The horse has a greater force with the ground and by pushing the ground back, the horse moves forward, along with the cart.
Nonparallel Forces
Nonparallel forces sounds like a pretty broad topic when you say it, and thats because it is. Nonparallel forces occur a lot in life. For example, when you're hanging something with a rope, nonparallel forces in those ropes are keeping the object suspended. Or when you are boating, the current or wind will change your direction. Below I will show you an example and further explain it.
Gravity and Tides
The Earth's natural tides can be explained through the pulls of gravity and Newton's 3rd Law.
Each day there are 4 tides in total:
>>2 high tides
>>2 low tides
Because the distances are different, point A and point B will experience different forces from the moon's pull. We know that Force and Distance are inversely proportional.
Therefore,
>>Since B has a greater distance, the force will be lesser
>>And since A has a lesser distance, the force will be greater
This difference in force is what causes a tidal bulge.
The sun is also effects the tides, but not nearly as much as the moon. However, specific alignments of the sun moon and earth cause different tides, called Spring and Neap tides.
When talking about tides you use the formula:
Which is the Universal Gravitational formula. Notice that distance is squared, unlike mass, that is why the moon has a greater effect than the sun on the earth's tides.
Momentum and Impulse Relationship
Momentum is defined by the letter p in physics, and it is equal to mass times velocity.
p=Mv
So, the momentum is directly proportional to the mass and velocity of an object.
An impulse is what causes change in momentum, and is also defined by the numerical change in momentum, which can be found with formula
J=p(fin)-p(int)
Impulse, or J is also defined by the formula
J=Force * Change in time
The Conservation of Momentum
Conservation of momentum states that momentum can be made or destroyed.
The two most important equations to remember when explaining conservation of momentum are for objects hitting and bouncing and objects and objects hitting and sticking.
When an object hits and bounces or explodes you use the following equation:
MaVa+MbVb=MaVa+MbVb
When objects stick you use the following equation:
MaVa+MbVb=Ma+b(Vab)
Good thing that the floor is squishy!
