Physics 10

Physics 10

•MONDAY APRIL 14th

• physics behind the knuckleball

• Physics PRE-ASSESSMENT Complete the true or false on page 1 of your Home Work Book 8 questions… do your best we will go over the answers.

(c) McGraw Hill Ryerson 2007

True or False

• 1) F, scalar quantities have only magnitude• 2) T• 3) F , If a trip takes you back to where you started, your

displacement is zero.• 4) F, distance is always greater or equal to the displacement• 5) T• 6) F, A straight horizontal line on a position time graph indicates the

object is not moving.• 7)F, The speed of an object is always greater than or equal to the

magnitude of its velocity.• 8) F , To calculate the acceleration of an object , you need to know

both velocity and time.



8.1 The Language of Motion

• Many words are used when describing motion.• Many of these words have specific meanings in science.• Some common words used to describe motion include:

Distance Time Speed Position

See pages 344 - 345

Describe the motion of the soccer ball before and after it is kicked.What key words did you use when describing this situation?

Kinematics

• All sports are a combination of athletic skill and science.

• In physics, the study of an object’s motion in terms of its change in position, velocity, and rate of change in velocity is called kinematics (derived from Greek – motion).

• Kinesiology: the study of human body movement.(c) McGraw Hill Ryerson 2007


Direction Makes a Difference

• Quantities that are measured or counted have a magnitude but may also contain a direction.• Magnitude refers to the size of a measurement or the amount you are

counting.

• Magnitude is simply the “size” of a quantity. Magnitudes are expressed in numerical form e.g., 450, 0.45,2/3 etc. Quantities that describe magnitude but give no direction, are distance, time

and speed.

Scalar

• Quantities that describe magnitude but do not include direction are called scalar quantities or scalars. Example: 25 seconds

• A common example of a scalar quantity is speed. Example: If a man is driving at a speed of 50km/h, we

say the magnitude of the scalar quantity is 50. Notice that the sentence “I am driving 50” is

incomplete. Therefore, the magnitude is equipped with a unit, in this case km/h.


Vectors

• Quantities that describe magnitude and also include direction are called vector quantities or vectors. Example: 5 km north Video clip


Every time you use a map or give directions, you are using vectors.

Question

•Question: What is the quantity that describes the length of a path between two points or locations?


• Distance (d) is a scalar quantity that describes the length of a path between two points or locations. Example: Olaf ran a distance of 400 m to reach his head.


Olaf

Distance

Question

•Question: What is the quantity that describes a specific point relative to a reference point?



Position

• Position ( ) is a vector quantity that describes a specific point relative to a reference point. Example: Sven galloped 1km east across the ice to reach

Olaf’s carrot nose.

See pages 346 - 347

d

Distance verses Position


• A car leaves home and drives 10 km to the store and then returns home. The car has driven a total distance of 20 km but its final displacement is 0 km.

• You drove to the store from your house. Describe the location of your car in relation to your house.

• Your distance driving to the store and back is _________?• Your position upon returning home if ________?

20km

0km

The cars position is 10km east.

Vector vs. Scalar


• You can always tell if a quantity is a vector because there will be an arrow drawn above it.Example:

• A scalar has no arrow.Example: The SI unit for both distance and

position is metres, m.

Northsmv /0.5

smv /0.5

SI Unit

•The SI unit for both distance and position is metres, m.


Summary so far

•Scalar•Distance - d•SI unit: metres

•Vector•Position - •SI unit: metres


d

Time

•Time (t) is a concept that describes when an event occurs.• Initial time (ti) is when

the event began.

• Final time (tf) is when the event finished.

• Example: The birthday party starts at 3pm.

• 3pm is the initial time for the party

• The party was over at 6pm.


Question

•Question: What is the term used for the difference between the final and the initial time?



Time Interval

•Time interval is the difference between the final and initial times.

See page 348

Time interval is calculated by: if ttt

•The symbol for a change in time or time interval is ∆t

Time interval example


ssst 325

• The time interval to move from the fire hydrant to the sign is calculated by:

The position of the sign is 7 m east of the tree.

SI Unit

•The SI unit for time and time interval is seconds, s.


• Question: You leave your class (t=0s) and walk to your car 50 m away (ti = 60s) and drive to Dairy Queen, have a chocolate cherry blizzard and return to school (tf = 2100s). What is your time interval?

• ∆t = tf - ti

= 2100s – 60s = 2040 s

• What is your position? Lets find out!



Displacement and Distance

• Displacement describes the straight-line distance and direction from one point to another. Displacement describes how much an object’s position has

changed. If the object ends up back where it started, its displacement is

Example: Your displacement from 0km to Dairy Queen and

back is

See page 349

Zero

Displacement


• Displacement is equal to the final position minus the initial position.

• The SI unit for displacement is metres, m.

d =

d f -

d i


• Question: For the skateboarder, in the time interval from 2 s to 5 s, the displacement is? •The skateboarder’s distance travelled is?

5 m [E]

Vector vs Scalar

• Since, it includes direction, displacement is a vector quantity. The symbol for displacement is


∆d

Summary so far

•Scalar•Distance - d

SI unit: metres

•Time – tSI unit - s

•Vector•Position -

SI unit: metres

•Displacement –SI unit – metres (m)


d

∆d

ح


Watch for Signs

See page 349

Common sign conventions

When using vector quantities, opposite directions are given opposite signs.

Example


• Between 0 s and 15 s the person’s displacement is

d =

d f -

d i

= 10 m [W] – 5 m [E]= -10 m – 5 m= -15 m= 15 m [W]

What distance did the person walk in this same time interval?

45 s

Question

• Is it a vector or scalar?Distance35 km [E]Time intervalposition


Question

• Explain what would be more useful to you if you needed to locate the shrink ray from “Vector”: the distance to the shrink ray or the position of the shrink ray? Answer: The position would be more useful since position

includes not only the distance the shrink ray is from the starting point but also the direction.


Complete

Term Symbol SI Unit Unit Symbol

Time Interval

s

Displacement Metre

d


∆t Second

∆d m

Position Metre m


•The End•Oh Yeah!

Activity

•With a partner get a lap top and complete the “graphing motion computer lab” assignment.

•What ever you don’t finish in class is Home Work.


Motion: 8.1

•TUESDAY APRIL 15th


Pre-assess

Do Questions Four on page 4 of 8.1 notes package. Graph the Data….

Questions Four


Is the Object in Uniform Motion?

NO, because the object travels different distances during different intervals of time.


Uniform Motion

•Objects in uniform motion travel equal displacements in equal time intervals.

•Objects in uniform motion do not speed up, slow down, or change direction.

See page 350

Uniform motion


The position of Wile E. Coyote in this photo is shown at equal time intervals. How would you determine if this motion is uniform motion?

Uniform Motion

• You can represent the motion of an object in a variety of ways. One way is: Wile E Coyote can be represented by a

motion diagram.


Motion Diagram


• A motion diagram shows the objects position at given times and allows us to picture or visualize motion.

0 cm 20 cm 40 cm 60 cm 80 cm 100 cm

t=0 s t= 1 s t= 2 s t=3 s t=4 s t=5 s


Graphing Uniform Motion

• Motion of an object can be analyzed by drawing a position-time graph.

See page 351

• The motion diagram allowed us to identify Wile E Coyote at corresponding time intervals. The data can be used to make the position-time graph.


Time (s) Position (cm [right])

0 01 202 403 604 805 100

Table: Position of Wile E Coyote

Graphing Uniform Motion

• A position-time graph plots position data on the vertical axis (y axis) and time data on the horizontal axis (x axis).


Uniform motion


•A straight line passing through the plotted data indicates uniform motion.

The straight line passes through all the plotted points.The straight line passes through all the plotted points.

Question?

•What is a best-fit line?


Best-fit Line

• Real motion is not perfectly uniform. ie. Measuring errors

• A best-fit line is a smooth curve or straight line that most closely fits the general shape outlined by the points.


•The best-fit line allows you to find the position of Wile E. Coyote at any given time.

•The motion diagram only provides Wile E Coyote’s position at 5 separate times.


Example of best-fit.

•Question: Find the position of Wile E. Coyote at 3.5 s


Best-fit line

•FYI: A best-fit line can also be extended beyond the first and last points to indicate what might happen beyond the measured data.



Slope

•The slope of a graph refers to whether a line is horizontal or goes up or down at an angle.

See pages 353 - 354Take the Section 8.1 Quiz

Question: What are the different types of slope?

Positive slope

•Positive slope Slants up to the right Indicates motion in the

direction of the positive y axis


Question

•An object travels 1.2 m forward in 3.0 s. If the object’s motion is uniform, what is its displacement during the next 3.0 s time interval?


Answer: 1.2 m forward

From the graph can you guess what type of slope

•Zero slope Horizontal line Indicates that

the object is stationary


Stationary golf ball

• For example: Golf ball is stationary 2 m to

the right of the hole Position-time graph-5.0 s

time interval would be a horizontal line

The golf ball at rest is an example of uniform motion. Why?

Because the displacement of the ball during any time interval is constant

(∆d = 0 m)(c) McGraw Hill Ryerson 2007

ح

One more slope

•Negative slope Slants down

to the right Indicates

motion in the direction of the negative y axis.


Example

• Suppose the golfer hits the ball too hard and it travels with uniform motion past the hole.

• The ball to the right of the hole would get a ___?__ value.

• The ball to the left of the hole would get a ? value.



Use the graph to answer the following questions


a) The object moves east with uniform motion.

b) The object remains stationary 6.0 m [E] for 3.5 m and then moves west with uniform motion for 0.5 s.b) The object remains stationary 6.0 m [E] for 3.5 m and then moves west with uniform motion for 0.5 s.

c) The object moves west with uniform motion

Watch for signs


a) 6 m [E]

b) 1 m [W]

c) 5 m [S]d) 0 m

Remember:Positives: North, Up, East and RightNegatives: South, Down, West and Left

d =

d f -

d i

•The End of 8.1


ACTIVITY:

• In a group of three complete the Slow Motion and Fast Motion Trial Lab on Page 358 of your text book.

• Complete the lab using Option A ( we are not using motion sensors today)

• Only three groups can collect data at a time, Mr Daniluck will select groups to come and collect the data.

• Graph Paper is available at the front.

• What you don’t finish in class is HOME WORK.(c) McGraw Hill Ryerson 2007

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Physics 10