Notes on: Linear (1-D) motion Calculating acceleration

Review Graphing Quiz: next class period

Reminders: 1) Formal Lab Report due Wednesday, 9/25/132) Pre-Assessment should have been completed online

Students will be able to:

Organize and evaluate data and make inferences from it using tables and graphs. (2J)

Generate and interpret graphs describing different types of motion. (4A)

Describe motion in one dimension using equations with the concepts of distance, displacement, speed, and average velocity. (4B)

Identify and describe motion relative to different frames of reference. (4F)

Students will be able to:

Describe linear motion and acceleration using the terms speed, distance, time, distance, displacement, scalar, and vector.

It is a change in position.

Frame of reference (FoR) determines how the motion is measured.

Ever been in a car at rest and suddenly thought it was moving because the car next to you started to move?

Ever been motion or sea sick?

These are all FoR issues. Your brain has trouble identifying the source of motion sometimes.

v = velocity (m/s)d = distance (m)t = time (s)

Speed = distance/timeVelocity = displacement/timeSometimes the answers are the same.

v = d/t This gives you an average velocity.

Total distance over total time. It doesn’t matter that the object doesn’t have an absolutely uniform motion.

Realize that you need to use significant digits in your answers.

Lots of students get confused on what they think of as “word problems.”

Physics is FULL of these things and so I offer you a way to improve your logic and reduce your stress.

It is NOT OPTIONAL.

Box 1: Record your data – what you know – with units. Box 2: Write the variable(s) for the unknown(s).Box 3: Give the original formula and then use algebraic manipulation if necessary to solve for the variable that is your unknown.Box 4: Show your work with units and give your calculator answer to extra precision.Box 5: Give the answer, with significant digits and units.

Given

Unknown

Equation

Substitute

Solution

1

2

A doctor travels to the east from city A to city B (75 km) in 1.0 hr. What is the doctor’s average velocity?

During a race on level ground, Andra runs with an average velocity of 6.02 m/s to the east. What distance does Andra cover in 137 sec?

•Simpson drives his car with an average velocity of 48.0 km//hr to the east. How long will it take him to drive 144 km on a straight highway?

How long? stopwatch

How far? Meter stick

How fast? speedometer

A toy robot walks 1.58 m in 3.22s. What is the average speed?

How long does it take a plane to travel the 1250 m of runway at an average speed of 85 m/s?

How long will it take a bowling ball traveling at 35 m/s to travel the full 18.25 m of the alley?

Acceleration is a change in speed – increase or decrease.

You can always tell when you are accelerating because you will feel a force.

Pushed forward, backward or sideways in a car or rollercoaster…

Because the speed is changing, you have two speeds to deal with now.

Acceleration can be positive – speeding up in a forward direction.

Or negative – slowing down in a forward direction.

It is also possible to be + = slowing down in a backward direction or – speeding up in a backward direction.

A toy car is at rest at the top of a ramp and gets up to 15 m/s at the bottom in 4.2s. What is the acceleration?

A plane hits the tarmac at 128 m/s and comes to rest in 18.2 s. What is the acceleration?

An object in motion tends to remain in motion in a straight line, and an object at rest tends to remain at rest until forces acting on it are unbalanced.

This is called the law of inertia.

Inertia is a resistance to a change in motion.

If an object is IN motion, the tendency is to STAY in motion, unless friction, air resistance or another outside force changes that.

If you release a bowling ball, it rolls in a straight line and at a relatively constant speed, so it has a constant velocity on release.

This is relatively unchanged until it hits the pins because the floor is highly waxed to reduce friction.

An object can be moving at a constant speed forward, backward, or it can be at rest (stopped).

The slope of the line does NOT mean the object is moving UP or DOWN.

d(m)

t (s)

d(m)

t (s)

A straight line on a distance-graph indicates that the object has a uniform or constant speed in a particular direction – velocity.

A horizontal line on a distance-time graph means that the object is at rest.

A velocity-time graph may resemble a distance-time graph but they are NOT the same thing.

v(m/s)

t (s)

d(m)

t (s)

Acceleration is a change in velocity / time

The object can change speed or rate of motion or

change direction

For now, acceleration = change in speed/ time

You can always tell when you are accelerating because you feel a force.

The acceleration of an object is proportional to the force applied.

F = ma

F = force (in newtons – N)m = mass (in kilograms – kg)a = acceleration (in m/s/s or m/s2)

An object is accelerating if the distance time graph is a parabola.

d(m)

t (s)

d(m)

t (s)

Speeding up in a forward direction.

Speeding up in a backward direction.

v(m/s)

t (s)

v(m/s)

t (s)

1) Plot the velocity-time graph of the motion. 2) Determine the distance the car travels during the first 2.0 seconds.3) What distance does the car travel during the first 4..0 seconds?4) What distance does the car travel during the entire 8.0 seconds? 5) Find the slope of the line between t = 0.0 sec and t = 4.0 sec. What does this slope represent?6)Find the slope of the line between t = 5.0 sec and t = 7.0 sec. What does this slope indicate?

Time (sec)

Velocity (m/sec)

0.0 0.0

1.0 4.0

2.0 8.0

3.0 12.0

4.0 16.0

5.0 20.0

6.0 20.0

7.0 20.0

8.0 20.0

1) Attend tutorials if needed. Tutorial schedule for all Physics teachers posted

2) Complete Great Graphing activity to prepare for quiz. Hand in at the beginning of class.

3) Complete the formal lab write-up. Graph outline provided. Due 9/25/13

4) Homework: Practice 2A p.44Practice 2B p. 49