Chapter 11 Notes – General Physical Science



Chapter 11 Notes – General Physical Science

Motion

Section 11.1 – Distance and Displacement

To describe motion accurately and completely, a frame of reference is necessary.

Frame of reference is a system of objects that are not moving with respect to one another.

Relative motion is movement in relation to a frame of reference.

- For example, if a train moves past a platform, people standing on the platform will see those on the train speeding by. But when the people on the train look at one another, they don’t seem to be moving at all.

Measuring Distance

Distance is the length of a path between two points.

Measuring Displacement

Distance is the length of the path between two points. Displacement is the direction from the starting point and the length of a straight line from the starting point to the ending point.

- For example, telling someone you walk 5 blocks does not give direction. If you tell the same person that you walk 5 blocks to school, you are now giving a displacement.

Combining Displacements

A vector is a quantity that has magnitude and direction. The magnitude can be size, length, or amount. Arrows on a graph or map are used to represent vectors.

- Add displacements using vector addition.

- When two displacements have the same direction, you can add the magnitudes together. Look at picture 3-A on page 330 in your book.

- When two displacements have different directions you must subtract the magnitudes.

When two or more displacement vectors have different directions, they may be combined by graphing.

Look at Figure 4 on page 331 and create a story that shows how a boy walked to school in the space provided below.

Resultant vector is the sum of two or more vectors. The resultant vector points directly from the starting point to the ending point.

11.2 – Speed and Velocity

Speed is the ratio of the distance an object moves to the amount of time the object moves.

- The units for speed are meters/second or m/s.

- Average speed is computed for the entire duration of a trip, and instantaneous speed is measured at a particular instant.

- The speed equation is….

Speed = distance

Time

- Where v = speed, d = distance, and t = time

Turn to page 333 in your book at complete math practice 1 and 2 in the space provided below.

1.

2.

Instantaneous speed is the rate at which an object is moving at a given moment in time.

Graphing Motion

A distance-time graph is a good way to describe motion.

- The slope of a line on a distance-time graph is speed.

Look at graphs A, B, and C on page 334 in your book. Draw and explain each graph in the space provided below.

A.

B.

C.

Velocity

Velocity is the speed and direction in which an object is moving.

- A change in velocity can be a result of a change in speed, a change in direction, or both.

Combining Velocities

Two or more velocities add by vector addition.

Look at page 337 and study figure A and B to help you understand this concept.

11.3 – Acceleration

The rate at which velocity changes is called acceleration.

- Acceleration can be described as changes in speed, changes in direction, or changes in both. Acceleration is a vector.

Acceleration applies to any change in an object’s velocity. This can be either an increase or a decrease in speed. A positive acceleration would be represented with a plus (+) sign and a negative acceleration would be represented with a (-) sign.

An example of acceleration due to change in speed is free fall, the movement of an object toward Earth solely because of gravity.

In the space provided below, draw the picture on page 343 in your book to show how free fall works.

Keep in mind that you can accelerate even if your speed is constant. If you are riding a carousel, your speed is the same but you are accelerating because you are changing direction.

Constant acceleration is a steady change in velocity.

Calculating Acceleration

You calculate acceleration for straight-line motion by dividing the change in velocity by the total time.

The equation is….

Acceleration = Final velocity – Beginning velocity

Time

Acceleration = a, units are meters/second2 or m/s2

Final velocity = Vf , units are m/s

Beginning velocity = Vi, units are m/s

Time = t, units are seconds or s

Turn to page 346 in your book and answer the math practice problems 1-4 in the space provided below.

1.

2.

3.

4.

Graphs of Accelerated Motion

The slope of a speed-time graph is acceleration.

A linear graph is one in which the displayed data for straight-line parts.

Draw a linear graph on page 347 in the space provided below.

This graph shows that a skier is moving at a constant acceleration.

Now draw a negative acceleration graph.

The line segment sloping downward represents the bicycle slowing down.

On page 348 you will find a accelerated motion graph. Draw this graph in the space provided below.

In a nonlinear graph, a curve connects the data points and it shows accelerated motion.

Instantaneous acceleration is how fast a velocity is changing at a specific instant.

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