Journal #7 Most missed question on the test: The total mass of four containers is 3.500kg. If A is 256g, B is 5917cg, and C is 382g, what is the mass of container D in kg? Show work Check Sig Figs

Name Period Chapter 2 Vocabulary Underline or highlight each of the 17 terms Place out on desk so it can be checked off

Chapter 2 Motion Notes

When does direction matter? In physics, all numbers are either scalar or vector quantities. Scalar - Have a magnitude and a unit, but do not indicate direction Ex.) distance = 5m, time = 10 s, etc. Vector - Have magnitude, unit, and a direction Ex.) displacement = 3m North, velocity = 2.5m/s NW, etc.

Why does direction matter? Consider the following question: Shelby runs 2 miles North and then 4 miles South. Determine the distance she traveled and her final displacement.

Shelby’s Distance To calculate distance, we add up the numbers that she has traveled (ignoring the direction b/c distance is a scalar). 2 miles + 4 miles = 6 miles

Shelby’s Displacement The first step in solving for any vector is to draw a vector diagram. A vector diagram is a simple drawing that represents the magnitude and directions of the vectors in the problem. All vectors are drawn as a single headed arrow with proportionate lengths and labels.

Shelby’s Displacement Which is the BEST vector diagram? origin 2mi N4mi S origin 2mi N 4mi S origin 2mi N 4mi S

Shelby’s Displacement Now, we must follow the rules of adding vectors. origin 2mi N 4mi S

Displacement Cont. The 3 Rules of Adding Vectors 1.Vectors in the same direction can be added together (keep the same direction) 2.Vectors in the opposite direction can be subtracted (the direction follows the larger number) 3.Vectors that are at right angles can be added using the Pythagorean Theorem

Shelby’s Displacement So, rule 1 doesn’t apply, but rule 2 is very important. 2mi N - 4mi S = 2mi S The answer of vector addition is called the resultant.

Another question Consider the following question: Hayden takes 3 steps forward, 2 steps to the right, 4 steps backward, 2 steps to the left. Determine the distance she traveled and her final displacement.

Hayden’s Distance To calculate distance, we simply add up the steps that Hayden took and end up with a total number = 11 steps (this number is always positive)

Hayden’s Displacement To calculate the resultant, we must start by drawing a diagram that represents Hayden’s movement from the origin. origin 3 forward 2 right 4 backward 2 left Notice that all vectors have a length and a direction when drawn

Displacement Cont. In Hayden’s problem, we cannot use Rule 1… none of the directions are the same. origin 3 forward 2 right 4 backward 2 left

Displacement Cont. Follow Rule 2 Forward and backward are opposites 3 forward - 4 backward = 1 backward Right and left are opposites 2 right - 2 left = 0 (no direction on zero) Because we are left with only 1 vector at the end of this step, we have found the answer (the resultant) to be 1 step backward.

Time Interval Time is a variable that we really have very little control over. Therefore, it is very important for us to be able to focus in on a small section of time during a problem. To find the time interval, we look at the final time and the initial time.

Time Interval Find the time intervals: The runner sped up from 4.5s to 8.5s = 4.0 seconds Class lasted from 10:31am to 11:25am 11: :00 = 25 min 11: :31 = 29 min = 54 minutes Helpful to use the hour as a midway point

Position-Time Graphs A position-time graph plots motion in comparison to time. If we limit our motion to 1 dimension, we can analyze movement very clearly from the graph. Slope (rise over run) is equal to speed on this type of graph

Mouse in a Tunnel

Make a copy of this graph

Understanding the Graph From 0-2s, the mouse moves forward. From 2-4s, the mouse moves forward but at a slower speed (smaller slope). From 4-6s, the mouse does not move (speed and slope = 0cm/s).

Understanding the Graph From 6-8s, the mouse moves backward. From 8-10s, the mouse moves backward at a faster speed (greater slope) and crosses the origin. From 10-12s, the mouse moves forward again ending back at the starting point (origin).

Journal # 8 Determine the speed of the object represented in the graph. Show all of your work.

The Speed Formula Remember that to calculate speed, distance, or time, we can use the speed formula.

The “Magic” Triangle distance in meters time in seconds Speed in m/s

Steps to working ANY problem in physics 1.Check the units, convert if necessary 2.Count the sig figs in the problem 3.Sketch a picture and label it 4.Define the variables 5.Choose a formula 6.Calculate the answer 7.Check answer for sig figs and unit 8.Check answer for vector or scalar properties

Example 1 A dog runs 25 meters in 15 seconds. What was his speed?

Example 1 A dog runs 25 meters in 15 seconds. What was his speed?

Example 2 A ball is rolling at a constant speed of 15 m/s. How long will it take for the ball to roll 150m?

Example 2 A ball is rolling at a constant speed of 15 m/s. How long will it take for the ball to roll 150m?

Example 3 How far have you traveled if you move at a constant speed of 55mph for 4.0 hours?

Example 3 How far have you traveled if you move at a constant speed of 55mph for 4.0 hours?

Example 4- Mixed Units A car travels at a constant speed of 10.0m/s for 2.0 hours. How far did the car travel during that time? Hint: Convert 2.0 hours to seconds

Example 5 A boy jogs for 45 minutes and travels 2.0km. What was his average speed in m/s? Hint: Convert 45 minutes to seconds and Convert 2.0 km to meters

Homework Questions Textbook: Page 39, #9, 11, 12 Page 41, #14-18 Page 42, #21-23 Page 53, #49-53, 56, 60 Due Monday 9/10

Homework Questions Textbook: Page 39, #9, 11, 12,Page 41, #14-18 Page 42, # Starts at m moves towards origin arriving at 5.0s 11. a. 4.0s b m 12. A starts West of High St. walking east, B East of High Street walking west intersecting after B crosses High Street 14. Runner A s 15. Runner B m m s m 18. a. 6.0 min b. No

Homework Questions Textbook: Page 53, #49-53, 56, 60

Homework Questions Textbook: Page 53, #49-53, 56, m (must show 2 sig figs) m min or 1100s min 56. a. 1.0h b. 45 min c km from origin 60. a. vary b s, s, and at 43.0s c. 9.0s,-1.00m/s

Silly Speed Problems Check 1.T=20s 2.T=2s 3.T=1000s, Does not make it 4.T=50s, Pikachu is eaten 5.T=0.4h or 24 min, Makes the show

Journal # 9

Journal # 10