|Note to the teacher: This lesson plan works especially well for middle school students, and parts of it may also be used for some high school classes. The unit is most appropriate for physical science, oceanography, and physics. While the lesson plan unit requires a lot of teacher confidence, you will find it a unit sure to be well received by your students.|
SUBTOPIC: Demonstration of Newton's Three Laws of Motion and the Law of Gravitation
The students will:
1) give examples of each of Newton's three laws as they occur in everyday experiences
Isaac Newton summed up motion in three laws. Today we take these laws for granted as we grow up assuming they are true. We do not realize the struggles scientists went through in attempt to understand the world around them. The following activities use brainstorming, discussion, and simple labs to illustrate the laws.
Newton's Three Laws:
1) An object which is moving at a constant velocity or at a state of rest does not change its state unless a force acts upon it.
MATERIALS: CHALK AND BLACKBOARD
1) Brainstorm everyday examples of the first law.
2) Present a lecture to students, including the following necessary background information:
Just prior to Newton's time Galileo had worked with the idea of acceleration. Galileo could only guess about time since precise clocks had not been invented. This is why he rolled metal balls down smooth ramps. Since he noticed how a ball slowed when rolling across the floor, he concluded that friction was the cause. Thus friction was responsible for the idea that objects in motion naturally come to rest. But 'rest' is just one kind of constant velocity. The concept of inertia and Newton's 1st law emerged from this insight.
3) Use some of the following examples to explain to the students how Newton's first law occurs in everyday events:
a) car suddenly stops and you strain against the seat belt
ACTIVITY #2 :
MATERIALS: METER STICKS, INDEX CARDS, TAPE, MARKERS
1) Newton's second law deals with F=MA. When written A = F/M on sees that the acceleration will vary directly with the force applied and inversely with the mass of the body. Since students have trouble with these terms, a simple visual aid can help them.
2) Take three index cards and write an A, F, and M on them, and then tape the F card to a meter stick at the 50 cm mark so that it hangs down. Next tape the A card at 0 cm and the M card at the 100 cm mark.
3) Explain to the students that if the force is constant (either flip the card up or cover it with your hand), when acceleration increases (raise the 0 cm end of the meter stick at a 30 angle) mass must decrease.
4) Note that the 100 cm end now angles down. This shows an inverse proportional relationship.
5) Now cover the acceleration card with your hand. When force or mass increases or decreases the other variable will do the same. This shows the direct proportional relationship.
6) Lastly, do the same for the M card.
7) Plug in numbers and work through some simple F=MA problems.
8) Use the meter stick to help visualize what the answer will be (greater or smaller). Finally brainstorm everyday applications, some examples are listed below.
a) hitting a baseball, the harder the hit, the faster the ball goes
MATERIALS: SKATEBOARD AND SPRING SCALE
1) Have a student bring in a skateboard.
2) Have one student stand on the skateboard at the front of the class and hold one end of the spring scale.
3) Another student should pull the first student at a constant force of 10 newtons.
4) Observe the speed of the students as they keep the force constant.
5) Explain that this shows the direct relationship
between force and acceleration.
MATERIALS: CHALK AND BLACKBOARD
1) Brainstorm everyday examples of the third law with the class. Listed below are some examples:
a) rockets leaving earth--many physicists of the nineteen hundreds (Goddard's time) said that rockets could never leave the earth. Discuss how a spaceship flies in space.
MATERIALS: 3 LONG BALLOONS, 1 PLASTIC STRAW, 60 CM (OR MORE) OF FINE WIRE OR FISHING LINE, TAPE, MODEL AIRPLANE (BALSA WOOD), MARKER
1) Have the students follow the procedures listed below:
a) Blow up balloons, fasten them with rubber bands, and label them A, B, and C.2) Have the students answer the following questions:
a) Describe the reaction of the rubber band when it was cut.
MATERIALS: PENCIL AND PAPER
1) Ask the students to write a 2 to 3 page science fiction story describing what differences we would observe if the opposite of Newton's three laws were true on earth. For example, guns would not have recoil, and a cannon's mass would not have to be greater than a cannon ball. You would also not be pushed back in your seat when undergoing acceleration in a car.
2) As an alternative, you may wish to do a verbal
brainstorming of how things on earth would be different if we lived under
the reverse of Newton's laws.
MATERIALS: CHALK AND BLACKBOARD
The gravitational force of the moon and sun play an important role in the tides. When the sun, earth, and moon are in a straight line, their combined gravitational pull causes extra high and low tides known as spring tides. Whenever there is a full or new moon this occurs. The neap tides form when the sun, the earth, and the moon form a right angle, causing a half moon. The question is which, the sun or the moon, has the stronger gravitational pull?
1) Using Newton's gravitational formula, have the students research (homework) the data needed and do a class project at the board doing the calculations.
2) Depending on the ability of the students, each
student may do their own calculations.
Mass of Sun 1.98 x 1030 Kg2) Explain to the students that the sun, therefore, should have greater pulling power. The tidal bulge produced by the sun is 46% of that produced by the moon. The tides are primarily caused by the gravitational pull of the moon. Besides the ocean tides, the moon also causes tides in the solid body of the earth as much as 25 cm. These earth tides are very hard to observe or detect. The water on the side of the earth near the moon is pulled toward the moon with a greater than average force, the water on the far side is pulled with a less than average force. In addition, the rotation of the earth helps raise a tidal bulge on the side away from the moon. Thus, two bulges appear in the water on opposite sides of the earth. Tidal bulges occur 3 ahead of the line which runs between the centers of the earth and the moon.
The pull between the sun and the earth is about 180 times stronger than the pull between the moon and the earth. So our calculations are correct, but why doesn't the sun cause tides 180 times greater? Because of the sun's great distance from the earth, there is not much difference in the distances from the sun to the earth's near and far side. This means that there is not much difference in the gravitational pull of the sun on the ocean nearest it and on the ocean furthest from it. The relatively small difference in pulls on the opposite sides of the earth only slightly elongates the earth's shape. Thus the sun produces tidal bulges less than those of the moon.
The tilt of the earth also affects tides. The tilt
causes the 2 daily high tides experienced in most parts of the ocean to
be unequal in height.
Additional Gravity Calculation for Honors Students
1) Since Jupiter is 7.8 x 1011m from the sun and has a mass of 1.8 x 1027Kg. Have the students calculate Jupiter's gravitational force, and determine if the sun produces tides on Jupiter.
F = 6.67 x 10-11 m3x 1.98 x 1030 Kg x 1.8 x 1027 Kg
MATERIALS: WATER, SMALL ROUND BALLOONS, AND STRING
1) Demonstrate the shape of the earth by first filling a balloon with water. It might be best to consider performing this outside, in the event that the balloon breaks.
2) Next, tie it shut and attach a string securely.
3) Swing the balloon around over head and observe the shape of the balloon. It should look elongated.
4) Explain that this is the same process which occurs on earth while it is rotating around the sun. The water covering the earth is distorted and will bulge like the balloon.
5) Read about the debate over the shape of the earth
between the followers of Newton and those of Descartes in Tom B. Jones,
Figure of the Earth, 1967.
MATERIALS: 2 CARTS, 2 PULLEYS, 2 HOOK MASS HOLDERS, 2 BARBIES, STRING, 2 BLOCKS OF WOOD (2X4X8")
1) Place a Barbie doll on each cart. On one of the carts, use a rubber band to securely attach the Barbie (seat belt).
2) Attach 2 meters of string to each cart. Attach 200 g. to the hook mass holder. Attach the pulleys to the table edge.
3) Place a block of wood in front of the pulley and place the string over the pulley.
4) Now attach the mass holder to the string while someone holds the cart in place.
5) Pull the carts back and allow the weight to accelerate
MATERIALS: 500 ML FLASK, 8 INCH EMBROIDERY HOOP, 10- 1/8 INCH NUTS
1) Balance an embroidery hoop vertically on the flask's mouth.
2) Stack nuts on the top of the hoop. Using one hand, snatch the hoop away quickly so that the nuts will fall into the flask.
3) Have students perform the activity and create a contest to see who can get the most nuts at once into the flask.
4) Relate this to Newton's first law and the famous
magician's act of pulling the tablecloth out from under the dishes.
Hewitt, Paul G. Conceptual Physics.