CIRCUS PHYSICS ACTIVITY GUIDE
Newton’s Laws of Motion
The Pound Puppies dog show looks like chaos in the ring, but the commotion can be explained
by Newton’s three laws of motion: objects in motion tend to stay in motion, force equals mass
times acceleration, and for every action, there is an equal and opposite reaction. In this unit,
students will learn how these three laws—Newton’s Laws of Motion—can help make sense out of
the outrageous antics of the dog show.
How to Incorporate the Video into Instruction
This video can be used to motivate the study of force, mass, and Newton’s Laws of Motion. It
can also serve as an extra illustration to reinforce previous lessons on these topics. If you
watch the video in class, ask students to pause the video at points where they see one of the
three laws of motion in action.
Questions to Ask Students Before Watching the Video
1.
2.
3.
4.
5.
What forces do you see in action?
Why does the dog slide down the slide?
What is happening when the dog jumps off of the man?
What force does the dog feel?
What force does the man feel?
Watch the Video: Newton’s Laws of Motion
http://www.pbs.org/opb/circus/classroom/newtons-laws/
Questions to Kick-Start Class Discussion After the Video
Write down Newton’s laws on the blackboard/whiteboard and ask students to watch the video
again, looking for instances of each law.
For fun you can write them as Newton did:
1. Every body perseveres in its state of rest, or of uniform motion in a right line, unless
it is compelled to change that state by forces impressed thereon.
2. The alteration of motion is ever proportional to the motive force impressed; and is
made in the direction of the right line in which that force is impressed.
3. To every action there is always opposed an equal and opposite reaction: or the mutual
actions of two bodies upon each other are always equal, and directed to contrary
parts.
Source: http://galileoandeinstein.physics.virginia.edu/lectures/newtongl.html
Group students into fours and ask them to brainstorm the different types of forces they see in
the video. Give the groups three minutes and then ask them to report back.
Ask students to think of times they have felt different forces.
different than balanced?
Do unbalanced forces feel
Unbalanced forces cause us to accelerate, which we naturally feel in our stomach and
chest. If students are having trouble, ask them to think about times they’ve been in
an amusement park.
Connections to Everyday Life
Most students will be familiar with acceleration from driving—stepping on the gas or slamming
the brakes. Another common experience of acceleration is jumping off of the diving board.
Look for local connections, such as skiing in northern states, and seismometers in earthquakeprone regions.
Suggested Classroom Activities
Activity 1: Pushing a Car
Students can estimate the mass of a car by doing a simple experiment, under adult
supervision of course. You’ll need a car, level ground, bathroom scales, chalk,
measuring tape, and stopwatches.
Have three strong students push the car. They will push the car from behind with the
bathroom scales between their hands and the car. Their goal is to push the car with as
constant a force—measured by the reading on the scale—as possible.
Another student sits in the driver’s seat to steer and operate the brake. A fifth student
sits in the front passenger seat and marks chalk lines on the ground at regular time
intervals. A sixth student sits in the back, calling out “mark” every two seconds, after
the “ready, set, go” has been announced.
From the changing distance traveled in each time increment, students can calculate
the car’s acceleration. You can find the speed over each interval, then look at how it
changes over the set of intervals. With the force measured from the bathroom scales,
and the acceleration, students can then estimate the car’s mass using F=ma.
When finished, the estimate of the car’s mass can be checked by looking at the posted
mass on the doorframe of the driver’s side, or by searching the Internet. Ask the
students to brainstorm the various possible sources of error in the experiment. You can
also film this for later video analysis.
Activity 2: The Constant Acceleration Race
If you have access to a gymnasium or open space, have students race to see who can
have the most constant acceleration. You’ll need ten students, each with their own
stopwatch, to stand at ten-meter (or yard) intervals. When the starter says “go” the
timers start timing and the runner runs down the track. As she passes each timer, that
person stops the stopwatch. A recorder then gathers the times from each timer.
Have five or so students run, and then ask the class to find each runner’s average
speed over each ten-yard interval. Have them graph this average speed versus time
and look at the slope of the curve. The curve with the most constant slope (closest to
CIRCUS Activity Guide: Newton’s Laws of Motion
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a diagonal line) will be the person with the most consistent acceleration, and the
winner of the race.
Activity 3: Newton’s Laws of Motion Video Analysis
To do this activity you will need to download the video “Video Point: Newtons Laws of
Motion” from the CIRCUS web site (http://www.pbs.org/circus/classroom/circusphysics/). Use VideoPoint (http://www.lsw.com/videopoint/) or similar software for
graphing and analysis.
Students will enjoy watching the motion of the dog’s antics and other videos using
VideoPoint. It is a great way to get them to specify exact locations that demonstrate
each of the three laws.
Look carefully at the following figure.
The red line shows the dog’s horizontal position as a function of time while the blue
line shows the vertical position.
The red graph demonstrates that an object in motion continues in motion, or Newton’s
First law. This is evident because the slope of the line never changes. The blue graph
demonstrates the second law, and shows the classic parabolic curve because the
motion demonstrates that an unbalanced force exists causing an acceleration. Have
students look for other examples.
CIRCUS Activity Guide: Newton’s Laws of Motion
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