Physics 11

Mr. Jean

February 7th, 2012

The plan:

• Video clip of the day

• HW Check

• Lab contracts

• Textbooks

• Position and movement

• Review of last day

• Constant acceleration equations

Homework Check:

• Re-arranging formula’s sheet. – Algebra– Scientific Notation

Lab Safety Contracts:

• Most people have passed this in however; if you have lost your copy there is a link on my webpage for you to print out.

• Also note: I’ve changed my website some to better accommodate cell phones. Let me know if this has helped.

Textbooks:

• How many people have their physics textbooks?

• If you do not have it get it soon!

Review of last day: Kinematics

• That branch of physics which deals with the motion of objects without reference to the forces which act on the system

• xi = starting location “initial position” (m)

• xf = ending location “final position” (m)

• vf = final velocity (m/s)

• vi = initial velocity (m/s)

• a = acceleration (m/s2)

• θ = angle in degrees

• t = time (s)

Important Variables:

Vectors & Scalars:

• Scalars are quantities we measure in everyday life. (Mass, time, energy etc…)

• In physics we normally describe motion in terms of vector. We have a quantity, but also a direction the quantity is travelling in.

• Distance and speed are scalars; however positive displacement, velocity, and

acceleration are vectors.

Scalars vs. Vectors:

Scalar Quantities Vector Quantities

Distance – 15km Displacement – 15km [N450E]

Speed – 30 m/s Velocity – 30m/s [S]

The basics of measuring motion:

Speed is measured in meters per second (m/s)

xi = starting location (meters)

xf = final location (meters)

ti = starting time (seconds)

tf = end time (seconds)

Speed:Speed = xf – xi

tf - ti

The basics of measuring motion:

Average Speed:Average Speed = Total distance (m)

Total time (s)

– Always measured in meters per second (m/s) for physics class.

The basics of measuring motion:

Velocity is a vector, thus you must give it a direction. The international SI unit for velocity is meters per second (m/s).

xi = starting location (meters)xf = final location (meters)ti = starting time (seconds)tf = end time (seconds)

Velocity: v = xf – xi

tf - ti

The basics of measuring motion:

a = acceleration (m/s2)vi= initial velocity (m/s)vf = final velocity (m/s)ti= Starting time (s)tf = End time (s)

Acceleration:Acceleration [Direction] = vf – vi

tf - ti

Constant Acceleration:

vf = vi + at

vf = Final velocity in m/s

vi = Initial velocity in m/s

a = acceleration in m/s2

t = time in seconds

Example #1• A slip and slide uses gravity to accelerate

people down a hill. On Ron’s awesome slip and slide people accelerate from 0m/s to 20m/s in 4 seconds. Find the acceleration in this situation.

Ron’s Slip and Slide

• What is Ron’s slip and Slide?

Example #2:• Hailey’s ball is rolling away from her at 2m/s. It start

to accelerate down a steep hill at the rate of 4m/s2 and continues to do so for 4 seconds. What is the balls final velocity?

Position & Distance:

• We need a “starting point”!

• This lets us describe the position in terms of fixed/pre-determined point. – Normally we make a reference point of (0, 0). – The position of an object is the separation

between that object and a reference point.– We use +, - to describe it’s relative position.

Position:

CBR – Motion detectors:

• Have you used the Ti-83 ranger motion detectors before?

• We are headed to the lab on Friday.

Constant Acceleration Equations:

• Let’s get back to some situational questions involving constant acceleration.

xf - xi = vi t + ½ (a) (t2)

xf = Final distance (m)

xi = Initial distance (m)

vi = Initial velocity (m/s)t = time (s)a = acceleration (m/s2)∆d = change in distance (m)

Constant Acceleration:

Example: xf - xi = vit + ½ (a) (t2)• Starting from rest at the start line Brandon roller

blades westwards with a constant acceleration of 2m/s2 for 15 minutes.

• What is his final distance?

Example: xf - xi = vit + ½ (a) (t2)• What is his final distance?

Example: xf - xi = vit + ½ (a) (t2)• Over the distance of 4000m Jessica’s car

accelerates at the rate of 30m/s2 [E] with for 15 seconds.

• What is Jessica’s initial velocity?

What is Jessica’s initial velocity?

To do:

• Text book readings – Read pages – p. 41 – 45– p. 47 – 49– p. 51 – 52 – p. 61 – 64

– Thursday we are in the lab.