Name Date

"r$ BeronE You Beclru

"NNewton's First Law of Motion states that an objectwill change its velocity onlywhen acted onby a force, but it doesn't say anything about how much the velocitywill change. A certain forceexerted on a baseball will have a much bigger effect than that same force will have on an apafi-ment house. Based on ordinary experience, the Greek philosopher Aristotle incorrectly believedthat the uel,ocity of an object is proportional to the force applied to it. He failed to understand oraccor-rnt for the effects of friction. Based on work done by Galileo, Newton discovered that theacceleration (A) of an object is proportional to the force (F) applied to it and inversely propor-tional to the object's mass (M). As an equation, this is expressed

^_FNote that force and acceleration are each vector quantities having both magnitude and direc-

tion, while mass is a scalar, which has only magnitude. Force is measured in neutons (N).The importance of this little equation is enormous. It can be used to predict accurately the

motion of a planet around the sun, a car on the highway, or a basketball on its way to the hoop.In this activity, you will see some of the practical implications of Newton's Second Law of Motion.Because it is very difficult to measure acceleration direcdy without special equipment, you willobserve acceleration i.nd,irectly In this activity, the maximum height reached by coins launched by

''

a falling weight will serye as an indicator of acceleration.

V/MnreRnLs% Ab""r 20 pennies

o Pencil. Jur, box, or other object 15 to ?0 cm tallo Thble or bench. Calculator (optional)o Graph paper (extension activity)

,o

@1.

Two wooden or strong plastic l2-inch rulers(one trtay be a meterstick)Transparent tape or white glue

PnocrDURE

Prepare three packs of pennies for the experiment as hoilows: Using glue or tape tojoin thepennies, make a pack with two pennies, a pack with three pennies, and a pack with five pennies.If this step is done the day before the main activity, use a drop of white glue between thepennies. If this step is done during the main activity, use transpaxent tape-as litde as possible-to hold the pennies together in a pack.Prepare the launcher. Set the pencil on the table, and place the lZ-inch ruler on top of andperpendicular to the pencil, with the pencil at the 7-inch mark of the ruler. The end of the longside of the ruler should be resting on the table, and the other end should be raised. Set thejarnear the raised end; the top of the jar will be used as a standard height from which to drop a

pack of pennies onto the raised end. Prop up or tape the se,cond ruler or meterstick to standuerti,cally behind and near the end of the long side of the first ruler. The second rulerwill beused to estimate the height reached by the launched packs. Have your partner positioned tosee both the meterstick and the launched coins. Position yourseHso thatyou can release thedropped pack onto the raised end of the ruler correctly and consistently. See Figure 1.

(conti,nued)

Ih.

@ 1999J. Weston Walch, Publisher 23 Walch Hands-on Sci,mce Seri,es: Force and Motion

Name Date

Figure 1

second ruler ormeterstick

launchedweight

pencil first ruler table

3. Place a single penny on the end of the long side of the ruler resting on the table. Hold the truo-penny pack directly above the raised end of the ruler at the height of the top of thejar, and dropthe weight. The single penny will be "launched" upward. Have your partner estimate the heightit reaches. Practice dropping and observing until you get consistent results each time. Be sure toreset the pencil on the table to the 7-inch mark of the nrler each time if needed. Then performthe experiment three times, recording the height reached by the single penny in the spaceprovided in the Data Collection and Analysis section. Calculate and enter the average of thethree trials

4. Repeat step 3 using the five-penny pack as the dropped object and the single penny as thelaunched object.

5. Repeat slep 3 with the five-penny pack as

launched object. .

the dropped object and the three-penny pack as the

Exrerustott Repeat step 3,launching the single pennywith the pack of three pennies. Recordyour results in the Data Collection and Analysis section. Now make a pack with four pennies.Repeat step 3, launching the single penny with the pack of four pennies. Record your resultsin the Data Collection and Analysis section.You have now launched the single penny with two,three,. four, and five pennies. Make a table of your results. Using the data in your table, make agraph of height reached (on the faxis) against force applied (on the xaxis) . Explain your result.

,dooto Cou-ecrott Rtrto AlRtvsrs\y

(continued) (D\i=/

Record your observations below.

Dropped Launched Height Reached

Trial I Tljal 2 Trial 3 Average

2 pennies 1 penny -cm CIn CIn

5 pennies 1 penny CIn -cm

5 pennies 3 pennies CM -cm

O 1999J. Weston Walch, Publisher 24 lr{alch Hands-on Scimce Series: Force and Motion

Name Date

VCorucLUDrNc QuesnoNsvWhen answering the questions, assurne

o that the height reached by the launched penny or pack is proportional to theacceleration it was grven.

o that the mass of a launched pack is proportional to the number of pennies it contains.. that the force applied to the launched pack'is proportional to the number of pennies

in the pack dropped from the standard height.

1. How does the acceleration of the launched pack depend on the force applied to it?

2.' How does the acceleration of the launched pack depend on its own mass?

3. The third assumption above is igelf an expression of Newton's Second Law. Explain.

"N Follow-up Activity ,NYou can see the effect of Newton's Second Law in everyday life-for example, when riding abicycle. To illustrate the dependence of acceleration on mass, think up an experimentusing abicycle, a backpack loaded with varying heavyweights, and a stopwatch. Write up the experi-ment so that others can try it.

@Motion

Dropped Launched Height Reached

Trial 1 Trial 2 Tkial 3 Average

3 pennies 1 penny -cm CM CIn

4 pennies 1 penny -cm CM CM

O 1999J. Weston Walch, Publisher 25 Walch lfands-an Science Seria: Fwce and