HONORS PHYSICS DAY 28 Here we go! Today: HW Quiz on the last HW’s We do great stuff with MOMENTUM We learn about IMPULSE We predict before we do math We learn about graphs

HW QUESTIONS? Answers up. Questions? Reminder: HW is for practice to make sure you are where you should be. Seek me for help. We are about to go fast, so if they are not making sense, see me. If you are behind, there is time to catch up. Get out the 3 HW’s for me. HW 4.3 HW 4.2 Hon Day in Class

HW QUIZ Only the 3 HW’s, no formula sheet or calulators.

Reminder: Watch this video of two cars colliding: There is a slight difference in impact speed between them. Get ready to answer some questions about it.

In both scenarios, did the hit car receive the same amount of momentum as the other scenario? A) Yes, Newtons 3rd law says that the forces are the same. B) Yes, these are isolated systems C) No, both cars impacted at different speeds, and moved different amounts D) No, it was not an isolated system

Is the car-car impact an isolated system? A) Yes, there was no outside force on the cars B) Yes, the cars are the objects before and after the impact C) No, the surface alone had an outside force on the cars as friction. D) No, the car-car system had outside forces and changed mass

How did the change of momentum of the hitting car compare to the change in momentum of the hit car? A) The same during the moment of impact, both in magnitude and direction. B) The same during the moment of impact, in magnitude but not in direction. C) Different due to it not being isolated.

How did the FORCE from one car to the other compare, along with the TIME they impacted? A) The amount of FORCE and TIME are the same during the impact. B) The amount of FORCE is the same, but the TIME of impact is different C) The amount of FORCE is different, but the TIME of impact is the same. D) The amount of FORCE and TIME different during the impact.

What if this was a big SUV vs. a smart car What if this was a big SUV vs. a smart car. How would the FORCE from one to the other compare along with the TIME they impacted? A) It would change because of the mass difference between the two things. B) It would not change even though the masses of the two things are different.

Car B travels left with a speed of 10m/s. Our example Car A has a mass of 1500kg and travels to the right at a speed of 20m/s. Car B travels left with a speed of 10m/s. After the vehicles collide, they stick together and move left with a common velocity of 5m/s.

Which car has more momentum, A or B? A) A! It has more velocity than B LOGIC Which car has more momentum, A or B? A) A! It has more velocity than B B) B! After the collision they are both going left, so B had more C) Don’t know until we do math

How much did Car A and Car B’s velocity change by? A) A changed by -15, B changed by 5 B) A changed by -15, B changed by -5 C) A changed by -25, B changed by 15 D) A changed by -25, B changed by -15 From 20 Right to 5 left is a change of 25!

B is 5 times as big, since it changed by 5 times less! LOGIC So if A changed by -25 and B changed by 5, how much bigger is B compared to A? B is 5 times as big, since it changed by 5 times less!

Our example Car A has a mass of 1500kg and travels to the right at a speed of 20m/s. Car B travels left with a speed of 10m/s. After the vehicles collide, they stick together and move left with a common velocity of 5m/s. 1. Calculate the mass of Car B Use your tables, do it on the blank slide to the side

Idea: Compare the momentums before and after

Lets Go Back, and determine the change of momentum for each

The CHANGE of MOMENTUM for a single thing is called the IMPULSE. In this system, both objects had the same IMPULSE, but in different directions.

So for the cars, lets say this occurred over a .5 second interval. We can use the CHANGE of MOMENTUM to find the FORCE with a time. On the next slide, lets do some math

Front Car Back Car Getting a from Vi, Vf and t Getting a from Vi, Vf and t Using Imbalance to get F Using Imbalance to get F

The CHANGE of MOMENTUM for a single thing is called the IMPULSE. IMPULSE: J It can be found through two ways: J

Front Car Back Car Using the Impulse: Using the Impulse:

So for the cars, lets say this occurred over a 2 second interval. On the next slide, lets do some math

Front Car Back Car Using the Impulse: Using the Impulse:

What is NOT set is the amount of FORCE it takes. If you slow down over a long time: The amount of force needed is SMALL. If you change over a quick time: The amount of force needed is LARGE

Showing this through bar graphs:

How can you tell this is an isolated system How can you tell this is an isolated system? Lets turn it into a non-isolated one

The change of momentum of a SINGLE object Idea In Words Impulse Symbol is Δp or J The change of momentum of a SINGLE object In Equation Units How its used Δp or J = Pfinal-Pinitial OR Δp or J = Fave*t Kg*m/s or a N*s During a change of motion, a force for a certain time causes that change in motion

How does the impulse of the person compare to the impulse of the box? A) The impulse of the person is larger than the impulse of the box B) The impulse of the person is equal to the impulse of the box C) The impulse of the person is less than the impulse of the box

How does the impulse of the person compare to the impulse of the box? A) The impulse of the person is larger than the impulse of the box B) The impulse of the person is equal to the impulse of the box C) The impulse of the person is less than the impulse of the box

How fast is the person going after the collision? Which idea is correct A) The persons change of velocity is equal to the box’s change of velocity B) The persons gain in velocity is 1/3 the box’s change of velocity C) The persons gain in velocity is 2/3 the box’s change of velocity

How fast is the person going after the collision? Which idea is correct A) The persons change of velocity is equal to the box’s change of velocity B) The persons gain in velocity is 2/3 the box’s change of velocity C) The persons gain in velocity is 1/3 the box’s change of velocity

WHAT IS WRONG HERE? 60kg 20kg 7m/s 0m/s 420 kgm/s 0 kgm/s 60kg 20kg V m/s 60*V kgm/s 20kg 5 m/s 100 kgm/s

CORRECT AND MAKE IT WORK 1)

What is his velocity after throwing the object?? (A)8 m/s (B)9 m/s (C)10 m/s (D)11 m/s (E)12 m/s

What is his velocity after throwing the object?? (A)8 m/s (B)9 m/s (C)10 m/s (D)11 m/s (E)12 m/s