Chapter 2

description of motion

-Where is the object now? (position) -Where is the object at a later time? (new time and new position) -how much material the object has? (mass)

free fall

-every object falls freely near earths surface -due to gravitational pull by the earth -gravitational acceleration due to earth near its surface. is 9.8 m/s^2 which is the magnitude of gravitational acceleration

g=

9.8 m/s^2

Scalar

A physical quantity that has magnitude only.

vector

A quantity that has magnitude and direction

True or False? Magnitude of displacement=distance

FALSE!!!!!

instantaneous acceleration

acceleration at a moment in time

velocity=

rate in change of position

acceleration=

rate of change of velocity

Distance is an example of a ...............quantity.

scalar

Scalar or vector? -distance

scalar

Scalar or vector? -speed

scalar

speed is scalar or vector

scalar

instantaneous velocity

the velocity of an object at some instant or at a specific point in the object's path

When you drop a crumpled piece of paper and a ball from the same height which will hit first?

they will hit at the same time

Constant acceleration represents: (a.) only magnitude is constant (b.) only direction is constant (c.) both magnitude and direction are constant

(c.) both magnitude and direction are constant

Investigate motion of objects

-point-like (mostly) -object that has mass -infinitesimal in size *Even though extended shap;e no harm treating as point particle

Description of motion

-where is the object now? (position) -where is the object at a later time? (new time) (new position) -how much material the object has? (mass)

Motion under constant acceleration rules

1. a=0: constant velocity 2. a=constant/uniform: average a=instantaneous a

Problem-Solving Strategy

1. read carefully to understand 2. draw a picture 3. write down quantities given 4. what are the unknown quantities 5. decide which equation can be used 6. write down that equation 7. manipulate the equation to isolate the unknown 8. plug numbers at the final step

What are the physical quantities of motion in one dimension?

Distance, displacement, speed, velocity acceleration

True or False? Negative acceleration is always deceleration

False -Deceleration always refers to acceleration in the direction opposite to the direction of the velocity. Deceleration always reduces speed. Negative acceleration, however, is acceleration in the negative direction in the chosen coordinate system. Negative acceleration may or may not be deceleration, and deceleration may or may not be considered negative acceleration.

Vector:

a quantity that is described by both magnitude and direction Displacement is an example of a vector quantity An arrow used to represent a vector has a length proportional to the vector's magnitude (e.g., the larger the magnitude, the longer the length of the vector) and points in the same direction as the vector.

Scalar:

a quantity that is described by magnitude, but not direction Distance is an example of a scalar quantity. Scalars are never represented by arrows.

instantaneous acceleration:

acceleration at a specific point in time

Deceleration:

acceleration in the direction opposite to velocity; acceleration that results in a decrease in velocity

acceleration due to gravity:

acceleration of an object as a result of gravity

acceleration

at what rate its velocity is changing

displacement

change in position

displacement=

change in position

motion

change in position of an object with time

Time:

change, or the interval over which change occurs

What is used to indicate position?

coordinate system

What is the formula for displacement?

deltaX=Xf- Xi

average velocity:

displacement divided by time over which displacement occurs Average velocity is displacement (change in position) divided by the time of travel,

average speed:

distance traveled divided by time during which motion occurs speed has no direction. Thus speed is a scalar.

distance=

distance traveled or total length moved

What are the physical quantities for motion in one dimension?

distance, displacement, speed, velocity, acceleration

True or False? Magnitude of displacement=distance

false

displacement=

final position - initial position

average velocity

for the whole motion. no information about velocity at any particular time

velocity

how fast the object is moving at a given instant in a certain direction

average velocity

how fast the object is moving in a certain direction

average speed

how fast the object is moving independent of direction

When two physical quantities are plotted against one another in such a graph, the horizontal axis is usually considered to be an ................... variable and the vertical axis a ................ variable.

independent, dependent

Scalar:

magnitude (only a number)

vector

magnitude and direction (a number and a +/- sign)

instantaneous speed:

magnitude of the instantaneous velocity

what are the units for velocity?

meters per second (m/s)

motion

most of the physical phenomena deal with; it is the change in position

Rotational motion

motion of a body that spins about an axis -Example: earth spinning on its own axis

rotational motion

motion of a body that spins about an axis. Ex. earth on axis

Translational motion

movement in which an entire molecule moves in a definite direction Example: a car traveling on a highway

translational motion

movement in which an entire molecule moves in a definite direction. Ex. car on a road

vibrational motion

movement of the atoms within a molecule in which they move periodically toward and away from one another -Example: A pendulum moving back and forth

vibrational motion

movement of the atoms within a molecule in which they move periodically toward and away from one another. Pendulum

investigate motion of objects

point-like (mostly) -object that has mass -infinitestimal in size -even though extended shape there is no harm in trating it as a point particle

Model:

simplified description that contains only those elements necessary to describe the physics of a physical situation

When you drop a flat piece of paper and a ball from the same height which will hit the ground first?

the ball (paper has too much air resistance)

Displacement:

the change in position of an object -Δx=xf−x0, where Δx is displacement, xf is the final position, and x0 is the initial position.

average acceleration:

the change in velocity divided by the time over which it changes

elapsed time:

the difference between the ending time and beginning time,

Slope:

the difference in y-value (the rise) divided by the difference in x-value (the run) of two points on a straight line

Position:

the location of an object at a particular time

Distance:

the magnitude of displacement between two positions Although displacement is described in terms of direction, distance is not. Note that the distance between two positions is not the same as the distance traveled between them. Distance traveled is the total length of the path traveled between two positions. Distance has no direction and, thus, no sign.

Acceleration:

the rate of change in velocity; the change in velocity over time

free-fall:

the state of movement that results from gravitational force only

Kinematics:

the study of motion without considering its causes

distance traveled:

the total length of the path traveled between two positions

dependent variable:

the variable that is being measured; usually plotted along the y-axis

independent variable:

the variable that the dependent variable is measured with respect to; usually plotted along the x-axis

distance

total length moved

3 basic types of motion

translational, rotational, vibrational

True or False? Distance is always positive

true

true or false? in free fall mass doesn't matter

true

Displacement is an example of a .................. quantity

vector

Scalar or vector? -acceleration

vector

Scalar or vector? -displacement

vector

Scalar or vector? -velocity

vector

Acceleration is a

vector in the same direction as the change in velocity, Δv . Since velocity is a vector, it can change either in magnitude or in direction. Acceleration is therefore a change in either speed or direction, or both. -So acceleration is in the same direction as the change in velocity, as is always the case.

instantaneous velocity:

velocity at a specific instant, or the average velocity over an infinitesimal time interval

position

where the object is now

Can an object have zero acceleration and non-zero velocity at the same time?

yes Think of a car traveling 65 mph and is not accelerating

The slope of a graph of velocity v vs. time t is acceleration a . slope=

ΔvΔt=a In this case, the vertical axis y is V , the intercept b is v0 , the slope m is a , and the horizontal axis x is t . Substituting these symbols yields v=v0+at.

The slope of the graph of position x vs. time t is velocity v . slope=

ΔxΔt=v

True or False? distance traveled always=magnitude of displacement

False -It is important to note that the distance traveled, however, can be greater than the magnitude of the displacement (by magnitude, we mean just the size of the displacement without regard to its direction; that is, just a number with a unit). For example, the professor could pace back and forth many times, perhaps walking a distance of 150 m during a lecture, yet still end up only 2.0 m to the right of her starting point. In this case her displacement would be +2.0 m, the magnitude of her displacement would be 2.0 m, but the distance she traveled would be 150 m. In kinematics we nearly always deal with displacement and magnitude of displacement, and almost never with distance traveled. One way to think about this is to assume you marked the start of the motion and the end of the motion. The displacement is simply the difference in the position of the two marks and is independent of the path taken in traveling between the two marks. The distance traveled, however, is the total length of the path taken between the two marks.

True or False? The direction matters when dealing with speed

False It is a scalar quantity. no matter which way you are going you are still going the same speed

True or False? Scalars are always represented by arrows

False Scalars are never represented by arrows.