Unit 4 FORCES AND MOTION

Objective  Understand how speed, velocity, and acceleration relate to motion of an object.  Analyze distance-time graphs and speed-time graphs.

Lesson 1  Motion  Question: Write in your notebook  1. How do you know something is moving?  Answer:  It goes from one place to another.  Question: Write in your notebook  2. How can you make something move?  Answer:  Things move when they are pushed or pulled.

Vocabulary Words Write in your notebook  Distance- the length between two places.  Position- its location compared to other things.  Motion-is the change in an objects position compared to a fixed object.  Speed-how fast an objects position changes with time at any given moment.  Velocity-is a description of moving objects speed and direction.  Acceleration-is the measure of change in velocity during a period of time.

Read pages  Distance and direction helps identify the position of something.  Apparent motion-when things appear to an observer to be moving but they are not actually changing.  Using distance and direction can help you identify the position of something.  If you ride in a car, you position changes compared to a fixed object such as a tree or a road sign.

Continued  Use apparent motion to determine what direction you are moving and to find out how fast you are moving.

Reading check pp. 181  Question:What are two things you must know to describe the relative position of an object?  Answer:  You must know the distance and the direction from a fixed location.  2. How can you tell which train is in motion if the train is in motion if the train next to the one in which you sit appears to be rolling backwards.?  1.

Continued  Answer:  Compare the position of both trains with the positions of objects outside that are not moving, such as buildings.

What is speed? Pp  Read the section as a class.  What is speed?  Speed is the distance an object moves in a unit amount of time.  What happens to your speed when you ride in a car?  Answer: you experience increasing speed constant speed or decreasing speed.  How to calculate speed  Speed=Distance/Time

Continued  Most moving objects do not travel at the same speed at all times.  Move away from a stop sign your speed increases.  Slow down when you park your car.  On page 182 compare constant speed and changing speed. (use the pictures)  A speedometer shows a car’s speed.  What is the bottom car’s speed at 6 s?

Distance and time graphs Page 18  Look at figure 3 on page 183. It shows the distance a runner might travel every second. Look at the line from left to right. According to the graph it took the runner 10 seconds to run 80 meters.  Now look at the second graph. Runner 1 ran at a faster pace than runner 2. the purple line is steeper that the green line. Steeper lines indicate faster speeds.  Look at the third graph. This graph shows that the speed of the runner is not constant. Notice a curved line.

Complete the reading check Questions pp. 183  Question  1. How can you find the average speed of a runner?  Divide the distance the runner covered by the time it took to run that distance.  Average speed=distance/time  Question  2. What is the average speed the runner of the runner show in the bottom graph in Figure 3?  Divide the total distance traveled by the time.  80 meters/9 seconds= 9m/s

What is velocity? Pp. 184  Read pages  Speed and direction are a part of motion.  Example:  If a car is moving west (direction) with a speed of 80 km/h (speed)  The car’s velocity is 80km/h west.  Look at figure the basketballs are bouncing. The arrows show the velocity. The changes in the arrow size mean that velocity is constantly changing. Velocity changes when the speed of an object changes.

Continued  If an object travels at a steady speed, its velocity is constant.  Any change in speed or direction causes its velocity to change.  Look at Figure 5 on page 185.  Both students are traveling at the same speed. But in a different direction.  The speeds are equal but different direction means they have different velocities because each student has a different direction.

Continued  Complete the Reading Check questions on page 185.  Question 1  What two pieces of information do you need to know to find the velocity of an object?  Answer:  You must know the speed and the direction.  Question 2  A marble hanging from a string swings back and forth. Describe how the marbles velocity changes as it swings.

Continued  Answer  The marble slows down and also changes directions as it swings back and forth. Eventually it stops.

What is Acceleration? Pp  When a car’s velocity is changing, it is speeding up.  An object accelerates when it velocity changes. (increases speed, decreases speed, or change in direction)  Notice in Figure 6 the arrows start short and then longer. That means the car has accelerated.  This means the speed has increased, so the velocity also increases.

Continued  The bottom car is slowing down. The arrow is shorter.  If the cars are going a constant speed the arrows will be the same length.  When the direction of the car changes its velocity changes.  When an object goes in the same direction, its acceleration can be calculated easy.

Continued  Formula:  Acceleration=change in speed/time  The change in speed is calculated from the starting speed to the final speed.  Acceleration has units per second. m/s/s which is meters squared.  If you increase your speed from 4 m/s to 6 m/s in 5s, you have increased your speed 0.4 m/s/s.

Continued  When you speed up your final speed will always be greater than your starting speed.  Reading Check Questions:  1. How can you calculate the acceleration of a commercial airplane?  Answer  Determine the change in the plane’s velocity over time.

Continued  Question  2. A car is accerlerating from rest at a rate of 5 m/s squared. How fast will it be going after 2 seconds.  Answer:  10 m/s  Read page 188  Understand the speed –time graph.  A the cheetah is not moving. B the cheetah is increasing speed from 0 to 30 m/s in 6 seconds. C the cheetah is maintaining speed. (no change) D the cheetah is slowing down.

Continued pp. 188  Reading Check:  Question  1. Explain how a speed-time graph can show acceleration.  Answer  By comparing speed on one axis and time on the other axis.

Continued  Question  2. The speed-time graph for an object shows a horizontal line, followed by a straight line that slopes downward to the bottom of the graph. What can you infer about the object’s motion?  Answer  The object was traveling at a constant speed with no acceleration until the sloped downward. Then the object decelerated (slowed down) until it came to a rest (stopped).

If time permits  Complete in your notebook page 189 questions Lesson 1 Review.  We will go over the answers next class period.  Homework which will be picked up and graded for a participation grade.  Lesson 1 Outline. Hand in next class period.  This will be turned to you for a quiz on section 1 on Friday or Monday.