Download Section 1: Measuring Motion

Chapter 10
Motion
Section 1: Measuring Motion

Motion – when an object changes its
position relative to a reference point
 Distance
– how far an object has moved
– distance and direction of an
object’s change of position from a starting
point
 Displacement
Section 1: Measuring Motion

Speed – distance an object travels per unit
of time
 Rate
– any change over time
 Calculation

 SI
for speed:
speed = distance/time
unit for speed is meter per second or m/s
Section 1: Measuring Motion
Section 1: Measuring Motion



Speed that doesn’t change over time –constant
speed
Speed is usually not constant; usually an object
has changing speed.
Average speed – speed of motion when speed
is changing:
 speed

= total distance/total travel time
Instantaneous speed – speed at any given
point in time
Section 1: Measuring Motion

A distance – time graph displays motion
of an object over time.
 1.
Plot distance on a vertical axis.
 2. Plot time on a horizontal axis.
 Slope = velocity

Velocity – speed and direction of an
object’s motion
Section 1: Measuring Motion
Section 1: Measuring Motion
Section 2: Acceleration

Acceleration—change in velocity’s rate
 Positive
acceleration—speed is increasing.
 Negative
 When
acceleration—speed is decreasing.
an object changes speed and/or
direction, it is accelerating.
Section 2: Acceleration

Calculating acceleration


1. Acceleration = change in velocity/time
2. Change in velocity = final velocity – initial velocity


Acceleration can have a negative sign
3. SI Unit for acceleration—meters per second squared

a = m/s2
Section 2: Acceleration

Acceleration can be graphed in a Velocity
– time graph
 Velocity
 Time
on y – axis
on the x – axis
 Slope
= acceleration
Section 2: Acceleration
Positive acceleration – positive number
with a positive slope on a velocity-time
graph
 Negative acceleration – negative number
with a negative slope on a velocity-time
graph
 Constant velocity – zero slope – flat line

Chapter 10.3
Motion and Force
Motion and Force

Force - a push or pull that one body
applies to another
 A force
can cause an object’s motion to
change.

Cause a change in acceleration and velocity
 When
two or more forces combine at the
same time, they create a net force.

Acceleration is in the direction of the net force.
Motion and Force

Balanced forces are equal in size and
opposite in direction.
 Does
not cause motion.
 Forces
cancel each other out.
Motion and Force

Unbalanced forces are unequal in size
and / or are not in the same direction.
 Causes
 A net
motion
force is created
The Force of Friction

Friction – force that opposes motion
between two surfaces that are touching
each other
 Microwelds,
areas where surface bumpers
stick together, are the source of friction.
 Friction
opposes motion.
The Force of Friction

Two types of friction
Friction – Friction between two
surfaces that are not moving past each other.
 Static
Friction – Friction between two
surfaces that are moving past each other.
 Kinetic
 Static
friction is greater than kinetic friction
The Force of Friction

Two types of Kinetic friction
friction – force that opposes the
motion of two surfaces sliding past each
other.
 Sliding
friction – Friction between a rolling
object and the surface it rolls on.
 Rolling
Force usually less than sliding friction.
 Cars could not move with out this type of friction.

The Force of Friction

Fluid Friction – force created by the
resistance of a fluid.
Friction and Motion

Harmful Friction can be reduced by 4
ways:
– substance that reduces friction.
 Ball bearings – creates rolling friction that is
less than sliding friction.
 Make surface smoother – reduces microwelds
 Make more streamline – reduces fluid friction.
 Lubricants
Friction and Motion

Helpful friction can be increased by:
 Make
 Add
surface rougher – increases microwelds
mass to increase weight