PHY FOR EXAM 1

Q: What is an order-of-magnitude estimate?

An estimate or calculation using about one significant figure. It gives a rough idea of the size of a quantity, not an exact answer.

What is the purpose of an order-of-magnitude estimate?

To get a quick, reasonable approximation without needing an exact calculation.

What does an order-of-magnitude estimate tell you?

It tells you approximately how large or small something is.

What type of numbers are usually used for order-of-magnitude estimates?

Rough numbers based on everyday experience.

1 kg

app 2 lb

1m

3 ft

1 in

3 cm

5 km

3 miles

1 m/s

2mi/h

What is the particle model?

A model where we treat an object as if all of its mass is concentrated at one point.

What is a motion diagram?

A diagram showing an object's position at different times using dots.

What does each dot in a motion diagram represent?

The object's position at a particular time.

If the dots in a motion diagram get farther apart, what does that mean?

The object is speeding up.

What is position?

Position tells you where an object is located relative to a chosen coordinate system.

What is a coordinate?

A number that tells you an object's location relative to the chosen origin.

What is displacement?

The change in position of an object.

What is the formula for displacement(delta x)?

final position(xf) - initial position (xi)

What does a positive displacement mean?

The object moved in the positive direction of your coordinate system.

What does a negative displacement mean?

The object moved in the negative direction of your coordinate system.

Is displacement the same thing as distance traveled?

No. Displacement depends only on the starting and ending positions, while distance is the total path traveled.

What is the meaning of t = 0?

It is the instant we choose as the starting/reference time.

What is a time interval?

The amount of time that passes between two events.

What is the formula for a time interval?

tf- ti

What does Δt mean?

Change in time / elapsed time.

What is velocity?

Velocity tells you how quickly an object's position changes and in what direction.

What is the formula for velocity?

v = Δx / Δt

What is the SI unit for velocity?

m/s (meters per second).

Is velocity a scalar or vector quantity?

Vector, because it has both magnitude and direction.

If an object has zero displacement, what is its average velocity?

Zero, because v=Δx/Δtv = Δx/Δt and Δx = 0.

Si stands for

international system of units

SI. unit of length

meter (m)

SI unit of time

second (s)

Si unit of mass

Kilogram (kg)

Why must every measurement include a unit?

Because the number alone doesn't tell you what quantity or scale you are measuring.

Example:
5 → unclear
5 m → clear

What are significant figures?

The digits in a measurement that are reliably known.

Why are significant figures important?

They show how precise or reliable a measurement is.

What is the main difference between multiplication/division and addition/subtraction rules?

• Multiplication/division → significant figures

• Addition/subtraction → decimal places

What is scientific notation?

A way of writing a number as a number between 1 and 10 multiplied by a power of 10.

What is the general form of scientific notation?

a × 10ⁿ, where 1 ≤ a < 10.

Write 1,270,000 in scientific notation.

1.27 × 10⁶

Write 0.00045 in scientific notation.

4.5 × 10⁻⁴

What does a negative exponent mean?

The number is small (between 0 and 1).

What is the diameter of Earth in scientific notation?

Approximately 1.27 × 10⁷ m.

What is unit conversion?

Changing a measurement from one unit to another equivalent unit.

What is a conversion factor?

A ratio that is equal to 1 and allows you to change units without changing the actual quantity.

What are the 3 basic SI units discussed in this chapter?

• Length → meter (m)

• Time → second (s)

• Mass → kilogram (kg)

What is the difference between speed and velocity?

Speed tells how fast; velocity tells how fast AND the direction.

motion

Position → Displacement → Velocity

formulas

Δx = x_f − x_i
Δt = t_f − t_i
v = Δx/Δt

how to solve multiplication scientific notation

4.5 × 10³ and 2.3 × 10^ 1

4.5 × 2.3 = 10^ 3+1

10.35 = 10^5

1.035 = 10^6

uniform motion

motion at a constant speed in a straight line

constant speed meaning

object moves at the same speed the entire time

straight line mean in uniform motion

the object does not change its direction while moving

If a car travels at a constant speed but keeps turning, is it uniform motion?

No. Uniform motion requires constant speed AND straight-line motion

what does speed tell us

only how fast an object is moving

what does velocity tell us

how fast an object is moving and its direction

speed is vector or scalar

scalar- it only has magnitude(how fast)

velocity is vector or scalar

vector- has magnitude (speed) and direction

average velocity

total displacement / by total time interval —- Δx / Δt

SI unit of velocity

m/s- meters per second

can speed be negative

no, speed is always positive and zero

what does the precision of a measuremetn tell us

It tells us how precisely we know the measurement.

Why are significant figures used in measurements?

To show which digits in a measurement are reliably known and communicate its precision.

What happens to significant figures when you take a root?

The answer should have the same number of significant figures as the least precisely known number in the calculation.

What is an exact number?

number with no uncertainity example - pie

In the equation d=2rd = 2r, is the 2 exact or measured?

Exact. It comes from the mathematical relationship between diameter and radius.

When converting a number greater than 10 to scientific notation, which direction do you move the decimal?

to the left

What determines the positive exponent when converting a large number to scientific notation

The number of places the decimal moves to the left.

Why is unit conversion especially important in physics?

Because different systems use different units, and calculations must use compatible units.

Why might you need to convert between SI and English units?

The United States commonly uses English units, while science generally uses SI units

What is the safe rule for calculations involving measured numbers?

Keep extra digits while calculating → round only the final answer.

vector

quantity that has both magnitude (size) and direction

magnitude

size or amount of a quantity

What is a complete description of a displacement vector?

Its magnitude AND direction, such as 50 m north.

When can you use the Pythagorean theorem for vectors?

When the vectors form a right triangle.

What is the Pythagorean theorem?

a² + b² = c²

In a right triangle, what does c represent?

The hypotenuse, which is the longest side.

how to find direction for displacement

by using trignometry

velocity vector

= direction of motion + speed

What are the two things every vector has?

Magnitude + direction

When adding successive displacement vectors, how do you arrange them?

Place them head-to-tail: the tail of the next vector starts at the head of the previous vector.

What does the final vector in a head-to-tail vector diagram represent?

he net (resultant) displacement, drawn from the starting point to the final point.

chapter 2

if an object is speeding up

its acceleration is positve or negative dpending on what direction of motion

units of acceleration is

m/s/s

time- s

velocity- m/s

for motion with xconstant, non0 acceleration, the postion vs time graph has the shape of

a parabola

A 1-pound ball and a 100-pound ball are dropped from a height of 10 feet at the same time. In the absence of air resistance, __________.

two balls end in a tie

Consider two graphs of velocity versus time for two objects in free fall. What can we say about the graphs?

the two graphs have the same slope.

The two graphs are both straight lines.

scalar quanity

quantity that has magnitude only. can descrive with number and unit

ex- mas-5g

time-10s

temp- 20 degree c

vector

has magnitude and direction

ex- 20 m/s east

5m north

si unit of velocity

m/s

Q: Why does average velocity use displacement instead of distance?

Because velocity includes direction, and displacement contains directional information.

Frank is at x = 25 m at t = 12 s. Five seconds later he is at x = 20 m. What is his average velocity?

First find displacement:

Δx=20−25=−5 m\Delta x=20-25=-5\text{ m}

Time:

delta t = 5 s

Therefore:

vavg=−55=−1 m/sv_{\text{avg}}=\frac{-5}{5} =\boxed{-1\text{ m/s}}

The negative sign means Frank is moving in the negative x-direction.

acceleration

rate at which velocity changes

why does an object have acceleration

because its velocity is changing

• this can happen because

• the object speeds up

• object slows down or

• the direction of motion changes

formula for acceleration

a= delta v/ delta t

si unit of acceleration

m/s ²

What does 7.5 m/s² mean?

The object's velocity changes by 7.5 m/s every second.

An object has an acceleration of 5 m/s² and starts at 0 m/s. What is its velocity after 3 seconds?

It gains 5 m/s every second.

After 1 s → 5 m/s
After 2 s → 10 m/s
After 3 s → 15 m/s

what does slope of a velocity vs time graph represent

acceleration