Bell Work: 3/18/14

T.O.C. #84. Speed and Motion Notes

Objectives

Apply proper equations to solve basic problems pertaining to distance, time, speed, and velocity (SPI0707.11.3)

Motion

Look around you- you are likely to see something in motion.

Even if you don’t see anything moving, motion is still occurring all around you.

Air particles are moving, the Earth is circling the sun, and blood is traveling through your blood vessels.

Motion

Motion is an object’s change in position relative to a reference point (the object that appears to stay in place).

Example: The hot-air balloon changed position relative to the mountain (a reference point).

Speed

Speed is the distance traveled by an object divided by the time taken to travel the distance. ◦S=d/t or S=d÷t◦Units meters per second (m/s) or kilometers

per hour (km/h)

An athlete swims a distance from one end of a 50 m pool to the other end in a time of 25 s. What is the athlete’s average speed?1.Write the equation for average speed.2.Replace the total distance and time with the values

given and solve.S=50m÷25s

S=2m/s

Velocity

Imagine that two birds leave the same tree at the same time. They both fly at 10 km/h for 5 min, 12 km/h for 8 min, and 5 km/h for 10 min. Why don’t they end up at the same place?

◦The birds went in different directions!

Velocity

Velocity is the speed of an object in a particular direction.

Speed and velocity are similar, but have different meanings.

If you say that an airplane’s velocity is 600 km/h, you would be incorrect. But you could say the plane’s velocity is 600 km/h south.

Acceleration

Although the word accelerate is commonly used to mean “speed up,” the word means something else in science.

Acceleration is the rate at which velocity changes over time.

An object accelerates if its speed, direction, or both change.

average acceleration=final velocity-starting velocity/time

average acceleration=5 m/s-1 m/s ÷ 4 saverage acceleration=4 m/s ÷ 4 s

average acceleration=1 m/s² south

Which of the following is NOT an example of acceleration?

A. a person jogging at 3 m/s along a winding path

B. a car stopping at a stop sign

C. a cheetah running 27 m/s east

D. a plane taking off

Acceleration

The momentum of an object depends on the object’s mass and velocity.

Calculating Momentum The relationship of momentum (p), mass (m), and velocity (v) is shown in the equation below:

p m x v

Momentum

Calculate the momentum of a 2.5 kg puppy that is running with a velocity of 2 m/s south. p m x v

P= 2.5 kg x 2 m/s south = = 5 kg m/s south

Momentum Practice

states that any time objects collide, the total amount of momentum stays the same.

The Law of Conservation of Momentum

Domino Derby

In this activity, you will observe one factor that affects the speed of falling dominoes.1. Set up 15 dominoes in a straight line (use the meter stick

as a guide). Try to keep equal spacing between the dominoes.

2. Use the meter stick to measure the total length of your row of dominoes, and record the length.

3. Use a stopwatch to time how long it takes for the dominoes to fall. Record this measurement.

4. Predict what would happen to that amount of time if you changed the distance between the dominoes. Write your predictions.

5. Repeat steps 2 & 3 several times using distances between the dominoes that are smaller and larger than the distance used in your first setup. Use the same number of dominoes in each trial.

6. Calculate the average speed for each trial by dividing the total distance (domino row) by the time the dominoes take to fall. S=d÷t

7. How did the spacing between dominoes affect the average speed?