Unit 3 Reflection

This unit, I learned about…

A.    Newton’s 3^rd Law and  Action/Reaction Pairs

• Newton’s 3^rd Law of Motion: “every action has an equal and opposite reaction.”
• Action Reaction Pair: Hammer pushes nail down, Nail pushes hammer up

B.        Tug of war/horse and buggy

• The Horse exerts a greater force on the ground than the buggy exerts on the ground, and therefore, the system is able to move.

C.        Forces in perpendicular directions

1. Draw Fgravity/Fweight straight down
2. Draw Fsupport Perpendicular to the GROUND
3. Draw Fnet

If done correctly, Fnet will be parallel to the ground and pointing downhill.

"Therefore, the box accelerates downhill."

D.        Gravity and Tides

Spring: Higher Highs
             Lower Lows
Neap:   Lower Highs
             Higher Lows

Gravity:

F=(Gm₁m₂)/d²
F=1/d²
x2 distance   = 1/4 original force
x3 distance   = 1/9 original force
x4 distance   = 1/16 original force
x1/2 distance= x2 original force
x1/3 distance= x9 original force
x1/4 distance= x16 original force

E.        Momentum – and Impulse momentum relationship

P=mv

Change in Momentum= P final- P initial

Change in Momentum= mv final-mv initial

Change in Momentum= Impulse

Impulse=(Force)(change in time)

J=Newtons
P=Kgm/s

Correct way to solve egg toss problem:

P=mv
Change in Momentum= P final- P initial

Regardless of how the egg is stopped, it will go from moving to not moving, therefore the change in momentum is the same, regardless of how it is stopped.

Change in Momentum= Impulse

Since the change in momentum is the same regardless of how the egg is stopped, the impulse is also the same.

J=Ft

The Winners increased the time it took to stop the egg, thus because the impulse is constant we can predict that the force will be less on the egg. A small force is less likely to break.

F.         Conservation of Momentum

****Individual objects can change their momentum, but systems cannot*****

Ptotal before=Ptotal after

Together in the Beginning:

m_av_a+m_bv_b = m_av_a+m_bv_b

Together in the Ending:

m_av_a+m_bv_b=m_a+bv_ab

Cart Problems:

****REMEMBER THAT IF THE CARTS ARE MOVING IN OPPOSITE DIRECTIONS, TO MAKE ONE OF THE VELOCITIES NEGATIVE***********************************************

Extra stuff:

Lab equation Steps:

1. Write equation of a line (y=mx+b)
2. Fill in y and x units (Ptotal before=slope(Vab))
3. Slope=___
4. Compare the theoretical to the actual slope
5. if close, yo confirm the law

Bouncing:

Bouncing creates more force. x2 impulse because 1 for stopping and 1 for pushing off. This is why police vests absorb bullets instead of bouncing them off.

Reflection:

What I have found difficult is remembering the simple things.

I have (hopefully) overcome these difficulties by writing myself disclaimers and making things I find tricky very noticeable.

I don't feel like me creativity, persistence, use of creativity, self-confidence in physics, skills in solving difficult problems, communicating both by my spoken and written words, collaborating with my group members, has changed since the first unit. I still feel confident, though the quizzes after the break took their toll on me a bit, but I think I am  back. It was just hard remembering all the things we had learned before the break, and then having no review time for what I, and the majority of the class, had forgotten. I think that I need to find better ways to not forget things.