Physics review

Displacement

change in position between 2 time intervals

Change in displacement= final - initial

has magnitude

arrow= vector

sign = direction

is time a vector

no

Scalar

just that # value like money

vector

has magnitude (speed=length) and direction,

Velocity Vector

rate of change of the position

BOLD= VECTOR

• v= Δr/Δt

Acceleration vector

rate of change of velocity

a = Δv/Δt

Ball thrown straight up

no matter what acceleration is always pointing down no matter what v looks like

Since velocity is going to the right and getting longer its speeding up so a is the same sign as velocity

since velocity is pointing left and slowing down a is the opposite sign bc its slowing

Finding position from velocity

MUST INCLUDE x_i

after finding vector/ force components how do you calculate Magnitude

add both x and y coordinates of all vectors together

eg

R_x = A_x + B_x

R_y = A_y + B_y

then using the final R_x and R_y find magnitude

SQRT(R_x² + R_y² )

after finding final total x and y components how do you find the angle of the resulting vector

tan(X)= R_y/R_x

X= tan^-1(R_y/R_x)

Kinematic equations

STUDY OF HOW THINGS MOVE

MAKE SURE TO USE THE SAME UNITS ONLY (m)

Acceleration:

• a_x(t)= a_x

• a_y(t)=a_y

• they’re constants

Velocity:

• (v_x)_f = v_x,i + a_xΔt

• (v_y)_f = v_y,i + a_yΔt

• linear

postion

• x_f = x_i + v_x,i Δt + ½a_x(Δt)²

• y_f = y_i + v_y,i Δt + ½a_y(Δt)²

• quadratic

v_f² = v_i² +2aΔx (CAN ALSO BE Δy!!!!!!!JUST CHANGE IN Y AXIS)

(v_x)_f = (v_x)_i

what does it mean when a= constant

position = parabola

velocity = linear

accel= flat line

What does it mean when a=0

position: linear

velocity: flat line

accel: 0

Free fall

all objects in free fall accel down at the sa,e rate

• caveat: this is only true if air resistance is very small

all objects in free fall acceleration

g = -9.8 m/s²

tips for kinematic equations

1. if there are 2 unknowns you must use 2 different equations to solve

2. define coord system

3. list all known

4. determine what to solve

what happens to vertica acceleration if I throw a ball horizontally

• nothing

• the ball will fall at the same rate even when thrown horizontally

  • vertical acceleration is unaffected by horizontal motion

perpendicular motions are

independent of each other

to calculate whats happening, first in one direction then the other

for projectile motion questions what does a_x and a_y equal to

a_x = 0

a_y = -9.8m/s²

How to find component velocity

(v_x)_i = v₀cosB

(v_y)_i = v₀sinB

Projectile motion concept, lets say I throw a rock down and one horizontally what is their accel

the same

record the time and you can find the height

Force

pushing/pulling action

Newton’s first law

• An object w/no forces on it and at rest, will stay at rest. An object with no forces on it that is moving will continue moving in a straight line at a constant speed

  • force is NOT required to maintain motion (often get it wrong bc normally friction slows things down)

  • resistance to change is called inertia

Newton's second law

units of force

name the forces

Long range forces:

1. gravity: w

2. electro magnetic:(dw abt this for now)

1. spring: F_sp

2. Tension: T

3. friction force: f, f_k, f_s

4. Drag: D

5. Thrust: F_thrust

6. normal: n

gravity/weight

spring force

tension force

Normal force

Friction force

Drag force

Thrust force

electromagnetic forces

Combining forces

tip to tail

how to find the acceleration of f net

How to solve free body diagram questions

whats the forces acting on this

Mechanical equilibrium

vector addition summary

what are the steps

1. 6in x 7in = 42in²

2. next convert all units to be the same: 1in =25.4mm → (1in)² = (25.4mm)²

3. now multiply the two values together: 42in² x 645.16mm²/1in²

4. 27096.72→2.7×10²

   1. 
      

WHICH WAY ACCEL GOING

If Sue walks home, what is her displacement if the cinema is the origin? Assume the positive direction is to the right.

Express your answer in miles.

-2,

this is because even though the cinema is the origin that doesn’t mean her current position changes

x_i= -3.2

x_f= -5.2

-5.2-(-3.2) = -2

how do you find velocity(aka average velocity) from just the length and time

• v= Δl/Δt

how do you convert the miles to time

miles/mph

Interpreting position-versus-time graphs

What is the rocket doing between

t = 100s and t = 400s?

ONLY WHEN ITS CHANGING SIGNS IS IT GOING DOWN THE OPPOSITE WAY

What height in km does the rocket reach before falling back to earth?

Express your answer in kilometers.

300, BECAUSE ITS THE INTEGRAL

DONT FORGET TO ADD THE x_i

_{it changes direction after crossing the x-axis}

How far does the pike move during this strike?

Express your answer in meters.

• because this question brings up velocity, acceleration, and time we know this is kinematics

• to find position use kinematic equation

• x_f = x_i + v_x,i Δt + ½a_x(Δt)²

=0.23m

what are the steps to solve this

1. convert cm to m

2. use v_f²=v_i²+2aΔy

3. v_f EQUALS 0 BECAUSE IT STOPS AT THE HIGHEST POINT ITS THE TURNING POINT MAXIMUM AND MINIMUM

GREATEST HIGH MEANS

velocity v_f= 0

first split the time in sec in half to find the max

A tennis ball is struck horizontally from a height of 1 m. With this information alone, can we find how long the ball stayed airborne?

YES

with no drag, horizontal velocity =

a_x = 0

vertical displacement equation

g IS POSITIVE

Horizontal Velocity

what equations do u use

vertical displacement, and horizontal velocity

TO FIND DISTANCE USING SPEED WHAT DO YOU DO

MULTIPLY TIME WITH THE SPEED

just use the vert displacement, bc its asking for how long it takes the ball to hit the floor dont think abt how its on the table, just from table to floor

part B of the last question, what formula do you use

the horizontal velocity one

When your car accelerates away from a stop sign, you feel like you're being pushed back into your seat.

INERTIA IS NOT A FORCE

Force formula

F=ma

mass= kg

f= N

a= m/s²

Tennis balls experience a large drag force. A tennis ball is hit so that it goes up and then comes back straight down. The direction of the drag force is

Down and then up.

A person gives a box a shove so that it slides up a ramp, then reverses its motion and slides down.

The direction of the force of friction is

Down the ramp and then up the ramp.

since force mass and accel given its F=ma

use it twice, 1 to initially find F then to find a using F

MAKE SURE ITS IN Kg

why is it incorrect

because there is no forward force applied to the ball, the ball is rolling freely on the table, forward motion is maintained by INERTIA and NOT a force

• there is no force vector to the right as it does not explicitly state contact with the club, what is maintaining the motion is INERTIA NOT FORCE

• drag is OPPOSITE of the motion

An ascending elevator, hanging from a cable, is coming to a stop.

Weight, tension

use tangent

Tension formula

T= mg

mass= kg

gravity +

use tension formula for 1

the use F=ma for the next and add the additional tension to the og

WHAT IS v_i

0, because at the top it hasnt moved yet v_f is the one that has velocity

what equations should u use

1. use x position first, finds time a=0

2. use y position, a= -9.8

a, because its pushed at CONSTANT SPEED

therefore, a=0, F_net=0 and all forces are equal on eachother

whats v_y,i

HORIZ VELOCITY IRRLEVANT

EITHER USE DISPLACEMENT FORMULA

OR REMEMBER FOR THESE Qs v_y,i IS ALWAYS = 0

by the end what are the weights of everything added up

3 children + 1 sled= 100kg