NEXT WEEK

HW Turn in occurring next week, along with our 2nd quiz event. A: Fri, B: Mon

LAB Due today, Turn-in date…Next time I see you

TODAY AT A GLANCE

AT THE START

A ball is dropped from rest near Earth. Neglect air resistance. Justify your answers

1) About how far will the ball fall in 3 seconds?

LETS GET VOTING!

A ball is dropped from rest near Earth. Neglect air resistance. Justify your answers

2) The same ball is dropped on the moon, where acceleration is 1/6 that of Earth. How far will the ball fall in 3 seconds? A) 1/6 as far as it did on Earth B) 1/36 as far as it did on Earth C) The same distance as the ball on Earth D) 6 times as far as the ball on Earth E) 36 times as far as the ball on Earth

KEY IDEAS WITH DETERMINING HOW A CHANGE AFFECTS A RESULT

Look at the equation. If the variable in question or the result variable are not direct (i.e. ½, squared, etc), then an increase/decrease is easy to determine.

LETS VOTE

A fish is able to jump vertically out of the water with a speed of 4.6 m/s. How much time in seconds does it take for the fish to pass a point 0.4 m above the water?

A) Unable to solve since there is not enough information to solve for the required variable.

B) Two possible answers since the fish reaches that height twice in its jump.

C) One answer possible that can be solved for using a kinematic equation with gravity as a.

NOW TO THE BOARDS

A panda throws two stones from the top of a building at 20m/s. One is thrown down, one is thrown up. Compare the accelerations of the two bricks

A) Both have same acceleration B) Thrown up has more acceleration C) Thrown down has more acceleration D) not enough info to solve

AND MORE

A panda throws two stones from the top of a building at 20m/s. One is thrown down, one is thrown up. The first one hits after time t1. How much later before the 2nd one hits?

A) 5s B) 4s C) 3s D) not enough info to solve

IN THE CASE

When an object is accelerating at a constant value, the average velocity will be equal to the instantaneous velocity

A) At the beginning of the time interval B) At the end of the time interval C) Halfway through the time interval D) ¾ of the way through the time interval.

KEY IDEAS WITH DEFINITIONS AND SCENARIOS. BACK TO YOUR SEATS

Draw number line or pictures to help you out.

Acceleration is how much your velocity changes by. So in the vertical direction, your velocity has-10 added every second when its in freefall.

As in the lab, average values = instant values in two situations At the middle of the time period Or at every point if there is no curvature of the

graph

LETS TRY ONE

In which case will a car move the greatest distance?

A) A car with speed V1 travels at constant speed for time t1 and accelerates to V2 in time t2.

B) A car with speed V1 accelerates to speed V2 in t1 seconds and then travels at speed V2 for t2 seconds.

C) Can’t do it without knowing all 4 values.

AND VOTING

You drop ball A from a building. 1 second later you drop ball B. As time progresses, the difference in their speeds

A) Increases B) Remains Constant C) Decreases D) Cannot be determined

VOTING

You drop ball A from a building. 1 second later you drop ball B. As time progresses, the distance between them

A) Increases B) Remains Constant C) Decreases D) Cannot be determined

SO FAR

You have seen how you need to know not just the definitions, but how they work in-depth.

Ex: Gravity just adding -10 to your velocity every second. But since displacement is dependent on the actual velocity at that moment, the amount of position you change depends on the starting velocity at that point.

X AND Y AND YOU AND ME AND OH MY

Reminder: X is horizontal, Y is vertical

Anything at an angle has X and Y parts called components.

Displacement, Velocity, and Acceleration are all vectors with Magnitude and Displacement

These components always point in the X and Y directions, with + and – directions.

The resultant, or overall, can be in any direction

A MAJOR IDEA

Consider the pull on the dog as two separate pulls… one up, one right.

If you pull more to the right, will the upward component change?

NO. The resultant and angle change though

THEREFORE

X motion and Y motion are independent. Something affecting X motion will have no

impact on Y motion

However, it will have an effect on the overall motion, since overall is a combination of X and Y

Pulls/Velocities/Displacements that have both X and Y parts (AND ARE THUS AT AN ANGLE) need to be separated into their X and Y components for analysis.

THINKING ABOUT…

A boat on a river. It has a velocity that it constantly goes at. (No acceleration) of 5m/s.

60m across

If the boat pointed straight across, how long would it take to cross?

If the boat pointed straight downriver, how long would it take to cross?

A boat on a river. It has a velocity that it constantly goes at. (No acceleration) of 5m/s.

60m across

Now, the boat is pointed so its still going 5m/s, but now at an angle.

The overall is still 5m/sThe X component is now 4m/sThe Y component is now 3m/s.

HOW LONG WOULD IT TAKE TO CROSS?

A boat on a river. It has a velocity that it constantly goes at. (No acceleration) of 5m/s.

60m across

Since the displacement is +60m in the Y, and the Y component is 3m/s, the time to cross (time to get from bottom to a top point) is 20 seconds.

What did the X velocity do to the boat in that 20 seconds?

Is the overall displacement of the boat in X, Y or both?

SO FAR

A X displacement can only use an X velocity and X acceleration. Same with Y.

A quantity at an angle must be broken in X and Y components to allow comparison.

Displacements, Velocities and accelerations ALL at the same angle and bearing can be compared without need for breakup.

A boat on a river. It has a velocity of 5m/s. There is a current shown at 2m/s.

60m across

Current

If the boat pointed straight across, how long would it take to cross?

The current in this case has no effect on the time, since the displacement is in Y, and current in X!

A boat on a river. It has a velocity of 5m/s. There is a current shown at 2m/s.

60m across

Current

What would the overall displacement of the boat be in the X and Y directions?X

Y

RELATING IT WEST VIRGINIA STYLE

What major physics idea so far is always going to be in either X or Y direction?

GRAVITY! Its only in the Y direction!

In the air: the acceleration in Y is -10m/s2. In the air, the acceleration in X is 0.

Synopsis: Since gravity pulls down, things in air won’t change speed horizontally.

IN DA HALL