Force & motion notes 2012

Teacher Friday, October 26, 2012 10:17:12 AM CT

When an object’s distance from another
object is changing.

You must have a reference point in
order to determine if something is in
motion.


Does the sun
move

Don’t copy or the Earth?
this slide.

The push or pull on an
object.


Force or attraction
between two
objects.


Gravity and Motion

• The gravitational
constant is 9.8 m/s².
• Objects fall to Earth
at the same
acceleration
regardless of mass.


Measure of the force of
attraction between an
object and Earth.

A Newton is the metric unit
used to measure weight.

Many forces act together on an
object.

However, it is not always
easy to determine what
is exerting a force or
what is receiving a force.


When forces are applied in the same
direction, the forces are added together.

Example: paddling a boat in the same
direction helps the boat to go faster.


When forces are applied in
opposite directions, subtract
the smaller force to determine
the direction.

Example: tug-of-war

The resulting force is called
the net force.


When a net force acts on an
object, the forces are
unbalanced.

This causes an object to start
moving, stop moving, or change
direction.

Equal forces on an object in
opposite directions are called
balanced forces.

This does not change an
object’s motion.

Force between surfaces that
resists the movement of one
surface past another surface.


Friction also exists
between an object rolling
across another surface.


Rate at which the position
of an object changes.


Two units of measure are required to
indicate speed.

1. Any unit of distance
Ex: centimeters, meters

2. Any unit of time
Ex: seconds, minutes, hour


A car travels at the speed of
65 miles per hour (65 mph)

The speed of an object moving in
a particular direction.

Includes both a speed and a
direction.


Why would an airplane traveling west at
750 km/hr have a different velocity than
an airplane flying southeast at 750
km/hr?

The speed may be the same but
the direction in which they are
flying is different.


Speed of a car:

65 miles/hour

Velocity of a car:
65 miles/hr to the west


The rate at which velocity is changing.

•Acceleration occurs when a moving
object speeds up, slows down, or
changes direction.


•Any change in velocity is acceleration.
•Slowing down is negative acceleration.

What would be an example of
positive acceleration?

A car going from 0 mph to 65 mph.


Acceleration
• Acceleration is the rate at which velocity
changes.
• A=V/t or the object’s velocity divided by
time.
• All objects accelerate towards Earth at
the rate of gravity.
• To calculate velocity of falling objects,
the gravitational constant is multiplied by
the time it takes the object to fall.


What affects acceleration?
• Air resistance is a
contributing factor to
acceleration.
• Air resistance is a fluid
friction that opposes the
motion of objects through air.
• The amount of air resistance
on an object depends on the
size, shape, and velocity of
the object.
• The more surface area an
object has, the more
susceptible it is to air
resistance.


Acceleration continues …
• As the speed of a falling object
increases, the air resistance
increases.
• This upward force of air resistance
increases until it reaches the
downward force of gravity.
• At this point the object stops
accelerating and continues falling at a
constant velocity called terminal
velocity.


Force & motion notes 2012

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