Chapter 6 Section 1

Chapter 6 Section 1



Explain the effect of gravity and air resistance on falling objects

Explain

why objects in orbit are in free fall and appear to be weightless

Describe

how projectile motion is affected by gravity

The

rate at which objects fall…

Galileo

questioned Aristotle’s idea about falling objects…

Mass

does NOT affect the time the object takes to fall to the ground

He

changed people’s understanding about gravity and falling objects



Objects fall at the same rate because:

 Acceleration

all objects!

due to gravity is the same for

 Heavier

objects experience greater gravitational force

 Heavier

objects are also harder to accelerate

Acceleration

= the rate at which velocity changes over time

All

objects accelerate to the Earth at a rate of 9.8 m/s²

For

every second an object falls, its downward velocity increases by 9.8m/s²

You

can calculate the change in velocity (∆V) of a falling object using: ∆V = g • t

g t

= 9.8m/s² = time it takes to fall (seconds)

Math

focus pg. 151 in text:

• Calculating the Velocity of Falling Objects • Sample problem… Now

it’s your turn… #1-4

Air

resistance = the force that opposes the motion of objects through air

Depends

on the size, shape, and speed of the object



As the speed of a falling object increases, air resistance increases

 The

upward force of air resistance continues to increase until it is = the downward force of gravity

 Net

force = 0; and the object stops accelerating

 The

object then falls at a constant velocity: Terminal Velocity

http://www.iop.org/activity/education/Projects/Teaching %20Advanced%20Physics/Mechanics/Images %20200/img_mid_4140.gif

An

object is in free fall only if gravity is pulling it down and no other forces are acting on it

Can

only occur when there is no air! (space & a vacuum)

Astronauts

float in orbiting spacecrafts because of free fall

Orbiting

= when an object is traveling around another object

When

a spacecraft orbits Earth, it is moving forward, but the spacecraft is also in free fall toward Earth

Space

shuttle is always falling while it is in orbit (Figure 7, pg. 154)

Astronauts

don’t hit their heads because they are also falling

They

float! (free fall with the spacecraft)

Circular

paths of orbits

Constantly

changing direction

The

unbalanced force acting on the object causing it to move in a circular path is called: centripetal force

Gravity

provides this force

http://www.mansfieldct.org/schools/mms/staff/hand/lawsCentripetalForce_files/image002 .jpg



Projectile motion: The curved path an object follows when it is thrown or propelled near the Earth’s surface

2

Components:

• Horizontal motion • Vertical motion 

When the 2 motions are combined a curved path is formed

A

frog leaping Water sprayed by a sprinkler A swimmer diving into water Balls being juggled An arrow shot by an archer…

http://www.cartoonstock.com/lowres/cal0008l.jpg

http://blog.dotphys.net/wp-content/uploads/2008/09/graph.jpg



After the object is propelled, the object’s horizontal velocity is constant

The

object’s vertical velocity increases because gravity causes it to accelerate downward

The

two motions combine to form a curved path

Perpendicular

to the ground

At

an acceleration rate of 9.8m/s² (ignoring air resistance)

Acceleration

on a thrown object and a falling object are the same

Aim

above a target!

Why

do you have to aim above a target that you want to hit with a thrown object?

When

does an object reach its terminal velocity?