Transcript Chapter 2 - Dublin City Schools

Chapter 2
Test Review
Newton’s First Law

Newton’s First Law of Motion

An object at rest will remain at rest
and an object in motion will continue
moving at a constant velocity unless
acted upon by a net force.
Motion
• Distance describes how far an object has
moved.
• Displacement is the distance and direction of
an object's change in position from a
reference point.
Motion

Motion

Change in position in relation to a reference
point.
Reference point
Motion
Speed & Velocity

d
Speed
rate of motion
 distance traveled per unit time

s t
distance
speed 
time
Speed & Velocity

Instantaneous Speed


speed at a given instant like on a
speedometer
Average Speed

the total distance traveled divided by the
total time of travel
total distance
avg. speed 
total time
Acceleration

vf - vi
a t
Acceleration
the rate of change of velocity
 change in speed or direction

a
v f  vi
t
a:
vf:
v i:
t:
acceleration
final velocity
initial velocity
time
Speed & Velocity

Velocity
speed in a given direction
 can change even when the speed is
constant!
 3 m/s north is an example

Speed & Velocity

Problem:

A storm is 10 km away and is moving at a
speed of 60 km/h. Should you be worried?

It depends on
the storm’s
direction!
Acceleration, Speed and
Velocity



Acceleration is the rate of change of
velocity.
Acceleration occurs when an object
changes its speed, it's direction, or
both.
A change in velocity can be a change in
speed or direction.
Acceleration


Positive acceleration
 “speeding up”
Negative acceleration
 “slowing down”
Newton’s First Law


Newton’s First Law of Motion
 “Law of Inertia”
Inertia
 tendency of an object to resist any
change in its motion
 increases as mass increases, decreases
as mass decreases
Graphing Motion
Distance-Time Graph
A



B


slope = speed
steeper slope =
faster speed
Straight (horizontal) line =
no motion
flat line = constant speed
Single point = instantaneous
speed
Force

Force
 a push or pull that one body exerts on
another
 What forces are being
exerted on the football?
Fkick
Fgrav
Force

Net Force
 unbalanced forces that are not
opposite and equal
 velocity changes (object accelerates)
Fnet
Ffriction
Fpull
N
W
N
Force

Balanced Forces
 forces
acting on
an object that
are opposite in
direction and
equal in size
 no
change in
velocity
 Net
force of 0
Balanced Forces



When two or more forces act on an
object at the same time, the forces
combine to form the net force
The net force on the box is zero
because the two forces cancel each
other.
Forces on an object that are equal in
size and opposite in direction are called
balanced forces.