Unit 3 Summary

Newton's 3rd Law and Action/Reaction Pairs

Newton's 3rd Law --> every action has an equal and opposite reaction

AS and CS pull each other with the same force due to Newton's 3rd Law that states, "every action has ann equal and opposite reaction". As you can see, the largest vector is "AS pushes ground right, and ground pushes AS left" because winning is not because of the pull, but rather the force on the ground. AS pushes harder on the ground, causing both teams to move left, so AS wins.

The big truck has a larger mass than the little car, but they have the same force on each other during a crash, because "every action has an equal and opposite reaction". Their equal force is justified by "big truck pushes little car, little car pushes big truck". Although, since the little car has a smaller mass its acceleration will be larger after the crash.

In this case, an apple is on a table and there are two action reaction pairs. The earth pulls the apple down, and the apple pulls the earth up. The table pushes the apple up, and the apple pushes the table down.

The horse pulls the buggy with the same force that the buggy pulls the horse, due to Newton's 3rd Law that states, "every action has an equal and opposite reaction". The only way a horse could pull a buggy would be if the horse had another interaction, and in this case that would be the ground. The horse must push on the ground with a harder force than the buggy pushes on the ground, so therefore both the horse and buggy would move in the horses direction to the right.

Forces in Perpendicular Directions 

 

Adding Non-Parallel Vectors

Boat "a" is going the slowest, but it's taking the most direct route.

Boat "c" has the longest vector so it has the faster ride, but it's route will take longer than boat "a".

Force of Gravity

This is the formula for the universal gravitational force.

G = (6.67) (10^-11)

You weigh less on a mountain than you do on the ground, because you're farther from the center of the earth.

Force is inversely proportionate to distance.

Force is also inverse square to distance.

Tides

Tides are caused by the difference in force felt by opposite sides of the earth. That force is determined by the distance from the moon.

As you can see, side A has a smaller distance from the moon, thus giving it a larger gravitational force. Side B has a farther distance from the moon, thus giving it a smaller gravitational force.

Side A and B feel different forces to the moon. Side A's net force will be towards the moon because of its strong gravitational force. In result, side B's net force will be away from the moon. This causes the tidal bulges. *It is
                                                                                    important to remember that if it was just the pull,
                                                                                    the sun would cause the tides, not the moon.

Spring tides occur when the sun, moon and earth are all in line. This occurs during a full or new moon. Spring tides cause higher than normal high tides and lower than normal low tides.

Neap tides occur when the moon is perpendicular to the sun and earth. This occurs during a half moon. Neap tides cause not as high tides and not as low tides.



There are two high tides and two low tides each day.
Each high tide and low tide are approximately 6 hrs apart.
Each high tide is approximately 12 hrs apart.
Each low tide is approximately 12 hrs apart.

Conservation of Momentum 

This is the equation for a collision where one object is moving with another object at rest, and one is moving with the other at rest in the second half of the equation as well. 

This is another equation for a collision with one object in motion and another at rest, but during the second half of the equation the objects become one moving force.

During a collision, you start out with some net force. During an explosion, you start out with no net force.

Since Newton's 3rd Law states that, "every action has an equal and opposite reaction" the force of object "a" will be equal to the negative force of object "b"

Similarly, the impulse of object "a" will be equal to the negative impulse of object "b"

 Similarly, the change in momentum of object "a" will equal the negative change in object "b"

So... the change in momentum of object "a" plus the change in momentum of object "b" will equal 0.

Why are cars built to crumble upon impact?

Cars used to be built with steel, but they are now built to crumble upon impact because it's safer.  With steel, the cars would come to an immediate stop during a crash. The car will go from moving to not moving no matter what surface it comes into contact with, so the ∆P will remain the same regardless of the surface because ∆P = mv and ∆P = P final - P initial. J = ∆P so if ∆P remains the same, then J will also remain the same. If J remains the same, then the time will increase and decrease the force on the car. Less force =  less injury.

Why do bullet-proof vests catch the bullets rather than reflecting them?

Bouncing requires two changes in momentum --> come to a stop and another to start again.

This means two impulses are needed because J = F∆ t  so two impulses means two forces. Bouncing will double the force than sticking.