Unit 3:Kinematics & Free Fall

Sprayberry

Physics

Physics Comp BookUNIT 3: Kinematics & Free-Fall Student will: compare algebraically the relationships between

time, distance, velocity and acceleration; compare and contrast scalar and vector quantities.

Page Contents 17 kinematics, free fall 18 gravity, gravitational acceleration, 19 air resistance 19 kinematics formulas—x and y directions 20 Ex: solving a kinematics problem 20 Lab SUMUP:

* How tall is the stadium?

p. 16

Frayer for kinematics

kinematics

describes the motion of objects without consideration of the causes leading to the motion

kinematics:

All the ways to describe motion in a mathematical way:

motion math

Example Problem:

time =

displacement =

velocity-initial =

velocity-final =

acceleration =

Kinematic Equations

Copy these into your comp book at the bottom of p. 19

2

)(2

22

22

tvvx

attVx

xaVV

atVV

fi

i

if

if

2

)(2

22

22

tvvy

gttVy

ygVV

gtVV

fi

i

if

if

Kinematic Equations - Ex #1

A car traveling with an initial velocity of 6 m/s, accelerates at 2 m/s2, for 6 seconds. What is the car’s final velocity?(1) LIST (3) Equation

(2) LABEL w/units (4) SolveAre we working in the x or y direction?

s

mV

atVV

f

if

18)6*2(6

Kinematic Equations - Ex #2

A car traveling with an initial velocity of 6 m/s, accelerates at 2 m/s2, for 6 meters. What is the car’s final velocity?

(1) LIST (3) Equation

(2) LABEL w/units (4) Solve

s

mV

V

V

xaVV

f

f

f

if

746.760

602436

)6*2*2(6

2

2

22

22

Kinematic Equations - Ex #3

A car traveling with an initial velocity of 6 m/s, accelerates at 2 m/s2, for 6 sec. How far does the car travel?

(1) LIST (3) Equation

(2) LABEL w/units (4) Solve

mx

x

attVx i

7236362

6*2)6*6(

22

2

Galileo Galilei

1564 - 1642 Galileo formulated the laws

that govern the motion of objects in free fall

Also looked at: Inclined planes Relative motion Thermometers Pendulum

Free Fall

All objects moving under the influence of gravity only are said to be in free fall Free fall does not depend on the object’s original

motion All objects falling near the earth’s surface fall

with a constant acceleration The acceleration is called the acceleration due

to gravity, and indicated by g

Acceleration due to Gravity

Symbolized by g g = 9.81 m/s2

g is always directed downward toward the center of the earth

Ignoring air resistance and assuming g doesn’t vary with altitude over short vertical distances, free fall is constantly accelerated motion

Free Fall – an object dropped

Initial velocity is zero Let up be positive Use the kinematic equations

Generally use y instead of x since vertical

Acceleration is g = -9.81 m/s2

vi= 0

a = g

Free Fall – an object thrown downward

a = g = -9.81 m/s2

Initial velocity ≠ 0 With upward

being positive, initial velocity will be negative

vi 0

a = g

Free Fall - example If a rock is dropped from a

building, and it takes 18

seconds to reach the ground, how tall is the building?

(1) LIST (3) Equation

(2) LABEL w/units (4) Solve

sec18

81.9

??

??

0

2

ts

ma

x

Vs

mV

f

i