# Near the surface of the earth

Document Sample

```					                         PHYS 1305 REVIEW GUIDELINES FOR EXAM 1

Chapter 1:

1. SI unit: Length in meters, Mass in kilograms, Time in seconds
2. Conversion of Units
3. Scientific Notation: Working with powers of 10

Chapter 2: Describing Motion

1. Average Speed: s = d/t (where s is the average speed, d is the total distance, t is the
total time) It can be expressed in m/s, miles/hr, ft/s, cm/s, etc.
From the above equation, d= s X t, and t= d/s. Instantaneous Speed = the average
speed over a time interval that is very, very small.

2. Speed with Direction: Velocity
V=          (where v is the average velocity, ∆x is change in displacement or total
displacement, ∆t is the time interval or total time.) Note that velocity is vector. A
vector is a physical quantity that has both magnitude and direction. Examples of
vectors are displacement, Examples are: distance, speed, length, population of
Houston, mass, how many, how much, how long, etc.
∆x = v X ∆t; and ∆t = ∆x/

3. Average Acceleration is a =∆v/∆t, a= vf – vi / tf- ti. That is the change in velocity divided
by the change in time.
(where a is the average acceleration, ∆v is the change in velocity, and ∆t is the time
interval or total time or change in time.) Instantaneous acceleration is the change in
velocity is change in velocity over a very, very small time.. Acceleration is expressed in
m/s2 .

4. Free Fall: What goes up must come down is due to the force of gravity acting on the
body near the surface of the earth drawing the body toward the center of the earth.
The force of gravity therefore is the force that planet earth exerts on any object on its
surface pulling the object downward toward the center of the earth. It always points
in the downward direction. Force of gravity has an acceleration g = -9.8 m/s associated
with it. Just as the force of gravity, the acceleration due to the force of gravity always
points downward. The force of gravity as well as its acceleration, decreases with
increase in altitude. Weight is the effect of the force of gravity acting on an object
pulling it downward. Therefore w= mg, where w is the weight expressed in newtons,
m is the mass expressed in kilograms, and g is the acceleration due to the force of

1
gravity expressed which has a value of -9.8 m/s2 near the surface of the earth.
Accordingly, weightlessness implies the situation where g, the acceleration due to the
force of is approximately equal to zero, which is the case in outer space. The weight
varies while the mass remains constant when an object is carried to outer space.

Chapter 3: Explaining Motion

1. Objects move because enough forces act on them. There are two types of forces:
contact forces and action-at-a-distance force or field force.
2. Remember Newton’s three Laws of Motion as stated in class. Know each of them very
thoroughly. Second Law equation is F = ma . Unit for force is Newton. IN = kg. m/s2 .
3. a = F/m, m = F/a.
4. Free-body/Force Diagram drawn isolating the body from its surroundings and showing
all the force, action and reaction forces, acting on the body and assuming the
directions of these forces.
5. Force of friction acts in the opposite direction to the force that causes motion. It is a
resistive force existing between two interacting surfaces. There are two types of
frictional forces: force of static friction, fs ≤µs n is the force that holds an object in
place or at rest. Motion takes place when applied force equals force of static friction.
Force of kinetic friction fs = µk n, this is the force that occurs when motion takes place.
It is a force that has one to contend with while motion is in progress. ( µs and µk are
called the coefficient of static friction and kinetic friction respectively and depend on
the nature of the two surfaces in contact and not on the area of the surfaces.)

Chapter 4: MOTION IN SPACE
1. When an object moves in circle, the displacement change ϴis circular in nature
2. Different parameters are used to express the velocity and the acceleration: ώand
α, respectively.
3. Centripetal acceleration, ac is due to the change in the velocity direction only and
it points toward the center of the circular path. That is why it is called center
seeking/pointing acceleration. Centripetal acceleration is produced by centripetal
force which also points toward the center. Centripetal acceleration, ac = v2 /r, Fc =
ma2 = mv2/r. Centripetal force plays numerous roles in circular motion.
4. Projectile motion is a two dimensional motion where the displacement, velocity
and acceleration has components in both the horizontal, X, and the vertical, Y
directions.

2
5. Motion is constant in the horizontal direction, that is velocity is constant in the
horizontal direction and there is no acceleration in the horizontal direction.
6. On the other hand, motion is not constant in the vertical direction, the vertical
component of the velocity varies because there is an acceleration in the vertical
direction, that is, g, the acceleration due to the force of gravity.
7. The maximum distance traveled by a projectile is called the Range, R= 2(Vocosϴ )t.  0
8. In general, a projectile motion is a mirror image of a free fall.
9. The motion of the rim of a bicycle tire and that car tire is called rotational motion.
10. Rotational motion is produced by a twisting force called torque. Therefore, torque
is a twisting force that causes rotation. Torque is responsible for most of the
external motion of the human body.

Chapter 5: Gravity

1. The concept of the force of gravity and its associated acceleration was clearly
explained by Isaac Newton. According to him, an object near the surface of the earth
falls down with an acceleration of 9.8 m/s every second. He also came up with the Law
of Universal Gravitation, F = Gm1 m2/r2 , where m1 and m2 are the masses of the two
objects. G, the constant = 6.67 X 10-11 N.m2/kg2= 0 .0000000000667 N.m2 /kg2 .
2. Near the surface of the earth, g = F/m= GME/RE2 . = 9.8 m/s2 , once we know the mass
of the earth. As mentioned above, g, varies with altitude. That means that a passenger
in an airplane flying many kilometers above the surface of the earth should weigh less.
3. Tides are caused by earth’s rotation and because of the bulginess of the surface of the
earth surface.

3
4
5.

5

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 0 posted: 10/3/2012 language: Unknown pages: 5
How are you planning on using Docstoc?