Matter in Motion

Chapter 5

Measuring MotionThe object that appears to stay in place is a

reference point.When the object changes position over time

when compared with a reference point, the object is in motion.

When an object is in motion describe the objects direction by using north, south, east, west, up or down.

Speed Depends on…..The rate at which objects moves is its

speed.Speed depends on distance traveled and

the time it takes to travel that distance.The SI unit for speed is meters per second

(m/s).Most objects don’t travel at a constant

speed so we use an average speed.The average speed is calculated by

dividing total distance by total time.

Lil….Speed…. PracticeA car travels the 180 miles from

Seattle to Portland at a constant 60 mph, then turns around and returns to Seattle at a constant 90 mph.  What is the average speed of the car during this trip?

   

AnswerSolution: The answer is not 75 mph as you might

mistakenly think.  The car takes 3 hours going to Portland and 2 hours returning so it spends a total of 5 hours traveling 360 miles for an average speed of 360/5 = 72 mph. 

If this seems odd, remember that the problem has the car traveling at two different speeds over the same distance, which is not the same as traveling at two different speeds for the same amount of time.  In this latter case you can indeed just average the two speeds to find the average speed.  But in our case, since the car spent a longer amount of time traveling at the slower speed, the average speed is closer to 60 mph than to 90 mph

Velocity: Direction MattersVelocity is speed in a given direction.Velocity gives distance, time, and the

direction of travel.Constant Velocity is always along a straight

line.Velocity changes if speed or direction

changes.Resultant Velocity is the combination of two or

more velocities.

1. Which car or cars (red, green, and/or blue) are undergoing an acceleration?

Study each car individually in order todetermine the answer.                                                                                  

AccelerationThe rate at which velocity changes is

accelerationThe faster velocity changes, the greater the

acceleration.Acceleration=(final velocity)-(starting

velocity)/time it takes to change velocityVelocity is expressed meters per second (m/s)

and time is expressed in seconds (s)How is acceleration expressed?

Examples of AccelerationPositive Acceleration: velocity increasesNegative Acceleration (Deceleration):

velocity decreasesSince Velocity has direction, the velocity

will change if the direction changes.A change in direction is acceleration, even

if there is no change in speed.

At what point does the car stop accelerating?

1. Which car or cars (red, green, and/or blue) are undergoing an acceleration?

Study each car individually in order todetermine the answer.                                                                                  

2. Consider the position-time graph at the right.

Each one of the three lines on the position-time graph corresponds to the motion of one of the three cars.

Match the appropriate line to the particular color of car

Answers 13. Goldie Goldfish, a speed swimmer, loves to race around the park’s

pond, which is 0.5 miles around. If she can swim 20 laps around the track in 2 hours, what is her average

speed? 20 x 0.5 = 10 miles ÷ 2 hours = 5 mph 14. It takes Stu, a slimy slug, 20 minutes to travel from his favorite bush

to the local trash can (a trip of 30 meters), how far can he travel in 1 hour (60 minutes)? 30 ÷ 20 = 1.5 m/min x 60 min = 90 m 15. At exactly 2:00 pm, Speedy the Snail crawls onto a meter stick at the

10 cm mark. If he reaches the 65 cm mark at exactly 2:10 pm, what is his speed? 65 cm - 10 cm = 55 cm ÷ 10 min = 5.5 cm/min 16. If it takes Leaping Louie 5 minutes to jump 3 blocks, how long will it

take for him to jump 15 blocks? 3 blocks ÷ 5 min = 0.6 blocks/min 15 blocks ÷ 0.6 blocks/min =

25 min 17. If Bert the Bat travels eastward at 40 mph with a tail wind of 6 mph,

what is his actual speed? 40 mph + 6 mph = 46 mph

Which of Newton’s Law

http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/newtlaws/cci.html

Newton’s first Law

Review of Newton Laws

Review of Newton Laws

2nd LawNewton's second law of motion pertains to

the behavior of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables – the net force acting upon the object and the mass of the object.

Force=Mass x Acceleration

Third Law of Motion While driving down the road, a firefly strikes

the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus?

Trick Question! Each force is the same size. For every action, there is an equal ... (equal!). The fact that the firefly

splatters only means that with its smaller mass, it is less able to withstand the larger acceleration resulting from the interaction. Besides, fireflies

have guts and bug guts have a tendency to be splatterable. Windshields don't have guts. There you have it.

 

4. In the top picture (below), Kent Budgett is pulling upon a rope which is attached to a wall. In the bottom picture, the Kent is pulling upon a rope which is attached to an elephant. In each case, the force scale reads 500 Newtons. Kent is pulling ...

a. with more force when the rope is attached to the wall.

b. with more force when the rope is attached to the elephant.

c. the same force in each case.

Answer C