PHYSICS
Units:
Analyzing Motion
Work and Energy
Waves
Electricity and Magnetism
TN Standards - Motion
• CLE.3202.3.1: Investigate the relationships among
speed, position, time, velocity, and acceleration
• CLE.3202.Inq.2: Design and conduct scientific
investigations to explore new phenomena, verify,
previous results, test how well a theory predicts, and
compare opposing theories
• CLE.3202.Inq.4: Apply qualitative and quantitative
measures to analyze data and draw conclusions that are
free of bias
• CLE.3202.Inq.6: Communicate and defend scientific
findings
Chapter 11 - Motion
• Sections:
• 1 - Measuring Motion
• 2 - Acceleration
• 3 - Motion and Force
1 - Measuring Motion
• Key Questions:
• How is a frame of reference used to describe motion?
• What is the difference between speed and velocity?
• What do you need to know to find the speed of an
object?
• How can you study speed by using graphs?
Frame of Reference
• Observe an object in relation to other objects that
stay in place, called reference points.
• A frame of reference is used to describe the
motion of an object relative to these reference
points.
• The trees in the background
in Figure 1
Distance
• Distance measures the path taken
• To measure distance, you measure the length of the
path that the object took.
• Displacement measures only the difference
between the final and starting positions
Speed & Velocity
• Speed – how fast an object moved
• Velocity – gives us both speed and direction
• Velocity is described relative to a reference point
• Up and right are positive; left and down are
negative ( Cartesian Coordinate system )
+y
-x
+x
-y
Motion
• When an object changes position with respect to
a frame of reference, the object is in motion
• Speed: Distance
travelled in a certain
time period
D
S
t
Calculating Speed
• Need two quantities – distance travelled & time
• Average speed – distance divided by time interval
• Instantaneous speed
– speed at a given time
– very small time interval
– Speedometer in car
D
S
t
Motion
• When an object changes position with respect to
a frame of reference, the object is in motion
• Velocity:
Displacement in a
certain time period
D
V
t
Demonstration
• Slope of a distance vs. time
graph equals speed
• Run a 6 m length ( in class? )
• Have your partner time you
• What is your speed?
Graphing Motion
• Sometimes easier to analyze motion on graphs
2 - Acceleration
• Key Questions:
• What changes when an object accelerates?
• How do you calculate the acceleration of an
object moving in a straight line?
• How can a graph be used to find acceleration?
Velocity Changes upon Acceleration
• Speed can change, but so can direction
• Notice speed is changing with each second
Changes in Direction
• Uniform circular motion has centripetal
acceleration
• Sources: friction, tension
• Demonstration
Circular Motion Demonstration
• Foam ball with string attached to it
• Swing ball with hand
• Diagram features of motion
• What happens when I let go of the string?
2 - Acceleration
• Key Questions:
• What changes when an object accelerates?
• How do you calculate the acceleration of an
object moving in a straight line?
• How can a graph be used to find acceleration?
BELLWORK
• What changes when acceleration occurs?
2 - Acceleration
• Key Questions:
• What changes when an object accelerates?
• How do you calculate the acceleration of an
object moving in a straight line?
• How can a graph be used to find acceleration?
Calculating Acceleration
V
A
t
Calculating Acceleration
• Acceleration is the rate at which velocity changes
• Acceleration is negative when slowing down
Graphing Accelerated Motion
• The slope of a straight line on a speed vs. time
graph is equal to the acceleration.
– Constant Acceleration
• Can also be seen from a distance vs. time graph
BELLWORK
• How do we calculate average acceleration?
3 - Motion and Forces
• Key Questions:
• What do scientists identify as the fundamental
forces of nature?
• What happens when there is a net force acting on
an object?
• What force always opposes motion?
• Why is friction sometimes necessary?
Fundamental Forces
• A Force is defined as any action that can change
the state of motion of an object
– Gravity, electromagnetic force, strong nuclear force,
and the weak nuclear force
• Fundamental forces vary in strength
• Forces can act through contact or at a distance
Balanced and Unbalanced Forces
• Whenever there is a net force acting on an object,
the object accelerates in direction of the net force
• Balanced forces do not change motion
• Unbalanced forces do not cancel each other
Friction
• Is a force
• Always opposes motion
• Static friction – occurs between
stationary surfaces
• Rolling friction
• Kinetic friction – occurs between moving surfaces
– Sliding friction ( usually greater than rolling fiction )
Friction and Motion
• Friction is necessary for many everyday tasks to
function properly
– Non-stick skillets
– Cars would not move without friction!!
• Can increase helpful friction or decrease
unwanted friction
– Sand on roads make them less slippery
– Lubrication reduces friction
Friction and Balance of Forces
• Cars do not or do move based on friction
– Constant speed
– Acceleration
– No Slipping
Demonstration – Spring Scale
• Drag wood and measure the force needed to
overcome friction ( various scenarios ):
• 1] single block of wood, wood-side down
• 2] single block of wood, sandpaper-side down
• 3] add another block to scenario #2
• 4] add something else to blocks ( your choice )
Questions
• What two factors appear to affect friction?
• What would make this experiment more
conclusive ( or how would you be more
confident in your data ) ?
Demonstration – Spring Scale
• Drag wood and measure the force needed to
overcome friction
• Friction depends on force applied between surfaces but
also surface roughness
• Rock keeps paper from being blown away by wind
• More weight on block  more friction
• Rougher surface  more friction