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VARIOUS NOTES: 'FORCES'

NEW BOOK   CHAPTER 18 SUMMARY

Chapter starts on page 522

 

WHAT IS MOTION?

 

All matter in the universe is constantly in motion

 

To describe an object in motion, you must first recognize that the object in motion. Something is in motion if it is CHANGING POSITION.

 

RELATIVE MOTION – Determining if something is in motion requires a POINT OF REFERENCE.

 

 

A POINT OF REFERENCE is a point to compare the object in motion to. Example: Take a step forward from where you are right now. After you have taken a step, look back at the exact point you moved from….MOTION has occurred  :0)

 

DISTANCE – How far something has moved

 

DISPLACEMENT – The direction and difference in position between your starting and ending points

 

 

SPEED EQUATION             SPEED = DISTANCE divided by TIME

EXAMPLE:  

DISTANCE:           An object traveled 20 centimeters

TIME:                    It took the object 5 seconds to accomplish this

SPEED:                20 centimeters (DISTANCE)       divided by       5 seconds (TIME) = 4 cms/sec

                                ***YOUR SPEED WOULD BE 4 CENTIMETERS A SECOND IN THIS CASE

 

 

An object can move at a CONSTANT SPEED which is the SAME EXACT SPEED over a certain time period.

 

An object can also change speeds at given times. In your car, your speed may be 30 miles per hour at one point, but then change to 35 miles an hour the next.   If you want to find your AVERAGE SPEED, take the TOTAL DISTANCE divided by the TOTAL TIME. It is the same basic formula.

 

INSTANTANEOUS SPEED is your SPEED AT AN EXACT MOMENT. For instance, if you are on a roller coaster, you might be traveling at 40 miles per hour one second and then 70 miles per hour the next.

 

You can easily graph changes in motion…..We will practice a few in class

 

VELOCITY – SPEED AND DIRECTION OF AN OBJECT

EXAMPLE: 

30 kilometers an hour east

55 centimeters a second north

92 miles a minute west

***If an object changes DIRECTION  OR  SPEED, it CHANGES VELOCITY. 

                                               

ACCELERATION is the CHANGE IN VELOCITY divided by the time it takes for the changes to occur. Like velocity, acceleration has direction.

 

Acceleration equation :       acceleration                (final speed – initial speed)

                                                                                                Time

 

***In short, take your FINAL SPEED minus your BEGINNING SPEED divided by TIME. Don’t let all of the numbers and letters scare you with this formula or any other formula!! J

 

Force =          Mass       *       Acceleration
(Newtons)  =  (KG)        *       M/S/S       (Meters per second squared)

COLLISIONS – Occur when a moving object collides with other objects

 

MASS – The amount of MATTER IN AN OBJECT   

The more mass it, the heavier that it is since gravity pulls on it harder

 

INERTIA – The amount of resistance to a change in motion as an object’s mass increases. What does this mean?? An object at rest will remain at rest. An object in motion will remain in motion.

 

MOMENTUM – This is a measure of how hard it is to stop an object. A dump truck going 30 miles per hour will be much harder to stop than a dog running 30 miles per hour. Therefore, the dump truck has greater MOMENTUM. 

***Sometimes it is not that easy to figure that out since things have different weights and travel at different speeds.

We can figure MOMENTUM out this way: 

Take the MASS (in kilograms) X VELOCITY (in meters per second)   MOMENTUM is symbolized as a ‘P’

 

 

CONSERVATION OF MOMENTUM – In ANY collision, momentum is transferred from one object to another.

 

THE LAW OF CONSERVATION OF MOMENTUM – According to the LAW OF CONSERVATION OF MOMENTUM, the total momentum of a group of objects remains constant unless outside forces act on the group.   Think about is this way, let’s say that you go bowling and knock down all 10 pins. The ball’s momentum is transferred to ALL of the pins.   Even though outside forces like friction and gravity have an influence on those things, OUTSIDE FORCES WILL NOT INLFLUENCE THE TOTAL MOMENTUM.

 

 

 

 PRACTICE TEST...ANSWERS ARE FAAAAAR BELOW....  GOOD LUCK!!!

 


PRACTICE TEST: MOTION


Section # 1

(1)    Rusty, a friendly neighborhood dog is sitting next to a park bench. A squirrel runs in front of Rusty and he tries to catch it. During the chase, Rusty sped up to 16                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     miles per hour in 4 seconds.  What was his average acceleration?  (NO SQUIRRELS WERE HURT DURING THIS PROBLEM :-)

A.            4

B.            4 mph

C.            4 miles/s

D.            4 mph/s

 

(2)     A mousetrap vehicle is waiting at the starting line to be released.  Once it is started, it accelerates to 40 centimeters a second in 4 seconds. What is its average rate of acceleration?

A.            10 cm/s/s

B.            40 cm/s/s

C.            0.1 cm/s/s

D.            0.1 mph

 

(3)You are flying through the air on a jet plane headed Hawaii on spring break  J   The plane was traveling at 700 kilometers per hour.  Over a period of 60 minutes, it sped up to 820 kilometers per hour. What is its average rate of acceleration?

A.            2 miles per hour

B.            1.24 km/hr/min

C.            1.2 miles per hour

D.            2 km/hr/min

 

 

(4)    You are roller-blading in the park at 50 meters per minute. Over a period of 1 minute, you speed up to a rate of 60 meters per minute. What is its average rate of acceleration ?

A.            1 mph

B.            1.2 mph

C.            1.2 m/min/sec/sec

D.            10 m/min/min

 

(5) Starting Velocity = 200 m/s
Final Velocity = 265 m/s
Time = 15 s
Acceleration = ___________

 

A.            4.33 m/s/s

B.            6.66 m/s/s          

C.            11 m/s/s

D.            11 mph

 

(6)    What is the force of a bowling ball that has a mass of 10 KG traveling at a rate of 4 meters/sec/sec?

A.            20 KG/M/S/S     OR  20 Newtons     (20 KG per meters per seconds squared)

B.            20 KG

C.            40 KG/M/S/S    OR  40  Newtons     (40 KG per meters per seconds squared)

D.            40 KG

 

(7)    What is the force of a 12.5 kg goose traveling at a rate of 2 meters/sec/sec?

A.            1 KG/M/S        OR  1 Newton    (1 KG per meters per seconds  squared)

B.            25 KG

C.            1  M/S

D.            25 KG/M/S      OR  25 Newtons   (25 KG per meters per seconds squared)

 

 

(8)    What is the acceleration of a speed boat that has a force of 900 Newtons and a mass of 100 KG?

A.            9,000 MPH

B.            9 MPH

C.            9,000 M/S/S  (9,000 meters per seconds squared)

D.            9 M/S/S         (9 meters per seconds squared)

 

 

(9)    What is the mass of a dog that has an acceleration of 9 M/S/S  and a force of 45 Newtons?

A.            5 GMS  

B.            245 GMS

C.            5 KG

D.            245 KG

 

(10)    If a runner travels 60 m in 6 sec, his average speed is

A.            60m/sec

B.            10

C.            10sec/m

D.            10m/sec

 

 

(11) Acceleration is measured in

A.            m/sec

B.            m

C.            m/sec/sec         or   meters per second squared

 

(12) A truck is going 0 miles per hour. It accelerates to 60 miles per hour in 6 seconds. Its average rate of acceleration is

A.            10 miles per hour per second

B.            10 miles per hour

C.            10 miles per second

 

(13) A wind-up toy travels 13 cm in 13 seconds. Its average speed is

A.            3 cm a second

B.            1 cm. A second

C.            3 cm

D.            1 second

 

(14)  A snail travels 30 cm in 300 minutes. Its speed is

A.   0.1 cm/min

B.   10 cm/min

C.    5 cm/min

D.   0.1 min/cm

 

 Section # 2

 

MATCH THE UNITS IN THE RIGHT-HAND COLUMN WITH THE TERMS IN THE LEFT HAND COLUMN

 

(15)        Distance                              A.               KG M/S

(16)        Speed                                   B.              M/S/S   or   meters per second squared

(17)        Acceleration                      C.             KG

(18)        Momentum                       D.            M/S

(19)        Mass                                     E              M

  

Section # 3

 

(20) An object’s momentum depends on its  ______ and ______

A.     mass, weight

B.      weight, inertia

C.     velocity, weight     

D.     mass, velocity

 

(21)   The  hands of a clock ______

A.     have a constant velocity

B.     have no momentum

C.     constantly change speed

D.     are always accelerating because they always change direction

 

(22) Acceleration =  Final velocity minus __________ divided by time

A.            Initial velocity

B.            Time

C.            Speed

D.            Mass

 

(23) Determining if something is in motion requires a ______________.

A.     Formula

B.     Point of reference

C.     Time

D.     Speed

 

 

(24)  Which of the following can occur when an object is accelerating?

 

A.         It speeds up

B.         It slows down

C.         It changes direction

D.         All of the above

 

(25)  Sound travels at a speed of 330 m/s.  How long does it take for thunder to travel 1,485 m?

A.         45 s

B.         4.5 s

C.         4,900 s

D          0.22 s

(26)  What is the distance traveled divided by the time taken to travel that distance?

A.         Speed

B.         Velocity

C.         Acceleration

D.         Inertia

 

 

(27) Speed WITH direction is _____________________.

A.         Speed

B.         Velocity

C.         Acceleration

D.         Inertia

 

(28) An object at rest will stay at rest. An object in motion will continue in motion, in a straight line, unless interrupted by an outside force.  This is the property of _________.

A.         Speed

B.         Velocity

C.         Acceleration

D.         Inertia

 

 

(29) All matter in the universe is constantly in ______________.

A.         Explosions

B.         Matter

C.         Distance

D.         Motion

 

 

(30) The direction and difference in position between your starting and ending points is _______

A.         Velocity

B.         Speed

C.         Displacement

D.         Mass

 

 

 

 

(31)  In ANY collision, momentum is transferred from one object to another. This is known as the Law of Conservation of ____________

A.         Velocity

B.         Speed

C.         Displacement

D.         Momentum


PLEASE DO NOT LOOK AT THE ANSWERS BELOW UNTIL YOU HAVE ATTEMPTED TO SOLVE ALL PROBLEMS

1      D
2      A
3      D
4      D
5      A
6      C
7      D
8      D
9      C
10      D
11      C
12      A
13      B
14      A
15      E
16      D
17      B
18      A
19      C
20      D
21      D
22         A
23      B
24      D
25      B
26      A
27      B
28      D
29      D
30      C
31      D 


*****Information taken from our school textbook   Glencoe Science Level Blue Book Copyright 2008