Transcript Look at your graphed line for “Experiment 1.”

Activity 78 Analysis
1. Look at your graphed line for “Experiment
1.” Explain why it does or does not indicate
that there is a relationship between force
and acceleration.
It does indicate a relationship because in
both experiments, as the force increases,
so does acceleration. In this case the graph
shows that the relationship between force
and acceleration is linear because the best
fit for the data set is a straight line.
2. Compare the two lines, “Experiment 1” and
“Experiment 2” on your graph. Identify and
explain:
a. any similarities.
The similarities are that both plots show a direct
relationship between force and acceleration,
both have straight lines that go through the
origin, and both have a positive slope. This is a
result of graphing the relationship F = ma when
the mass is held constant. In this situation, force
versus acceleration will always be a straight-line
graph that goes through the origin and have a
slope equal to the mass.
b. any differences
The major differences in the graphs is that
the second plot has a steeper slope. The
slope on “Experiment 2” is steeper than
the slope from “Experiment 1” because the
mass is 4 kg in “Experiment 2” and the
mass is 2 kg in “Experiment 1”.
3.
Use your equation for force, mass, and acceleration to
find the missing values in the table below.
Experiment 3
Force (N)
Mass of
Block (kg)
25
5
Acceleration
of Block
(m/s2)
5
20
2
10
10
5
2
50
10
5
100
4
25
1,000
40
25
4. In the first activity, Vehicle 2 has greater
acceleration than Vehicle 1, but has a
less forceful engine. How can this be?
Explain in terms of your equation.
Vehicle 2 can have a greater acceleration
with less force if it has a lower mass than
Vehicle 1. Newton’s equation F = ma, can
be rewritten as a = F/m, which shows that
acceleration is the ratio of force to mass.
Thus, for an object to obtain a higher
acceleration with less force, it must have
less mass.
5. One newton of force is the same as 1 kg x
1 m/s2. Use your equation to explain why
this makes sense.
Since force, measured in newtons, is
equal to mass times acceleration, the unit
of force, must be equal to the unit of mass
(kg) times the unit of acceleration (m/s2),
which is known as the compound unit of
kg- m/s2.
Activity 78 Major Concepts
• There is a direct relationship between
the force applied to an object and its
resulting acceleration.
• When an object is subject to a force,
there is an inverse relationship between
its mass and its resulting acceleration.
In other words, with the same applied
force, an object with a smaller mass will
have greater acceleration.
Activity 79
Title: Inertia Around a Curve
Read E-25
Problem: How does inertia affect how
an object moves?
Hypothesis: If _______________, then
____________________.
Moving and Changes in Motion
• Moving is any change in position.
• What is a change in motion?
• A moving object does not necessarily
have a change in motion. An object
traveling in a straight line at a constant
speed is moving (changing position),
but in not changing its motion (not
accelerating) because neither its speed
nor its direction is changing.
Inertia
• Which type of car, a heavier or lighter
one, needs more force to slow down
with the same deceleration?
A car with more mass needs more force
to slow it down.
Copy this into your notebook!
Background information:
Inertia IS NOT a force. It is a word that
describes the tendency of an object to
keep moving on its current path and at
its current speed.
Qualitative vs. Quantitative
• Today is a qualitative day.
• We will be making observations that do
not include recording numbers or
measuring distances or times.
• Take your time with your observations.
Demonstration
http://www.youtube.com/watch?v=6gzCeXDhUAA
&feature=related
Review Procedure
Possible Pitfalls
• Irregularities on the table and any spin on the
marble may cause the marbles to veer from
its intended path.
• The path of the lower mass glass marble is
more likely to be affected by forces applied to
it after it leaves the track.
• If you are having trouble getting consistent
results, send the marble around the track at a
higher speed.
• Make a barrier around your table with
books and rulers
• Don’t tell me you lost your marble. Find
it. It is somewhere. Mass is neither
created nor destroyed.
Follow-up
• Read and compare analysis questions 1
and 2
• The term inertia describes the tendency
(and not the force) of an object to keep
going in a straight line at a constant speed
even when there are no forces acting on it.
• How do the sides of the circular track wall
affect the motion of the marble?
• What happens when the marble exits the
track?
After Data/Evidence, compile a list of all
changes in motion of the marble and
name the forces that were responsible.
List of Forces Responsible for Change of
Movement
Change in Motion
Force Responsible
Homework
• Answer Analysis questions 1-3
• Be ready to trade and grade PH
assignment from Tues/Wed on Monday
• Update Vocabulary