Kinematics in Physical Science-Hightower
From wiki.NGSciEd.org
Contents |
Grade Level Targeted
Grades 9-11 in Physical Science
GPS Addressed
SPS8 Students will determine relationships among force, mass, and motion.
a.Calculate velocity and acceleration
b.Apply Newton’s three laws to everyday situations by explaining the following: inertia; the relationship between force, mass and acceleration; and equal and opposite forces.
c.Relate falling objects to gravitational force.
SCSh1 Students will evaluate the importance of curiosity, honesty, openness, and skepticism in science.
e.Exhibit the above traits in their own scientific activities.
f.Recognize that different explanations can often be given for the same evidence.
g.Explain that further understanding of scientific problems relies on the design and execution of new experiments which may reinforce or weaken opposing explanations.
SCSh2 Students will use standard safety practices for all classroom laboratory and field investigations.
b.Demonstrate appropriate techniques for all laboratory situations.
SCSh3 Students will identify and investigate problems scientifically.
a.Suggest reasonable hypotheses for identified problems.
b.Develop procedures for solving scientific problems.
c.Collect, organize, and record appropriate data.
d.Graphically compare and analyze data points and/or summary statistics.
e.Develop reasonable conclusions based on data collected.
f.Evaluate whether conclusions are reasonable by reviewing the process and checking against other available information.
SCSh4 Students will use tools and instruments for observing, measuring, and manipulating scientific equipment and materials.
a.Develop and use systematic procedures for recording and organizing information.
SCSh5 Students will demonstrate the computation and estimation skills necessary for analyzing data and developing reasonable scientific explanations.
e.Solve scientific problems by substituting quantitative values, using dimensional analysis, and/or simple algebraic formulas as appropriate.
SCSh8 Students will understand important features of scientific inquiry. Students will apply the following to inquiry learning practices:
a.Scientific investigators control the conditions of their experiments in order to produce valuable data.
b.Scientific researchers are expected to critically assess the quality of data including possible sources of bias in their investigations’ hypotheses, observations, data, analysis, and interpretations.
Background
Students learn about air resistance when they learn about friction and Newton’s second law of motion. Newton’s second law of motion states that “the acceleration of an object is in the same direction as the net force on the object” (McLaughlin, Thompson, & Zike, 2008, p. 69). The more force that is exerted on an object, the more acceleration it will have. The more mass an object has, then the less acceleration it will have than a less massive object if the same amount of force is exerted on the objects. Thus, “force, mass, and acceleration are related” (p. 68). “If the body is subject to multiple forces at the same time, then the acceleration is proportional to the vector sum (that is, the net force)” (In order to figure out the acceleration of an object in meters/second2, you divide the net force (in newtons) by the mass (in kilograms). The equation is: a = Fnet/m and can be rewritten to say F = ma.
Friction is a force that opposes the sliding motion of two surfaces. This occurs on a microscopic level. Surfaces that appear to be smooth are rough, and when two surfaces come in contact, microwelds form between them where the rough bumps of the surfaces come in contact. “The larger the force pushing the two surfaces together is, the stronger the microwelds will be” (p. 71).
There are three basic kinds of friction: static friction, sliding friction, and rolling friction. Newton’s first law of motion states that an object in motion will resistant changes to that motion unless a force is exerted on it. This inertia means that in order for a moving object to stop, some force must act on it. Static friction prevents two surfaces from sliding past one another. In this case, the net force on the object is zero and acceleration is zero, because the object doesn’t move. Sliding friction opposes the motion between two sliding surfaces. Without sliding friction, sliding objects would continue to move due to inertia until some force made the object stop. Rolling friction occurs between the deformed area between a wheel and its surface contact and causes rolling objects to stop.
Air resistance is a friction-like force that opposes the motion of objects that move through the air. Gravity pulls falling objects down towards Earth, and air resistance acts upward on falling objects. The greater the surface area is, the greater the air resistance acting on an object. Without air resistance, falling objects would fall with the same acceleration – the acceleration due to gravity, but “air resistance causes objects to fall with different accelerations and different speeds” (p. 73).
Integration of Science Concepts
Students will be looking at motion as it relates to falling objects. They will observe the forces of gravity and air resistance acting on an object and finding ways to maximize the upward force of air resistance. In this manner they will better understand how the characteristics of objects affect how they fall and react to the force of air resistance. They will also indirectly explore how objects fall with the same acceleration if air resistance is not a contributing factor.
Management Considerations
When students drop their air resistant creations, watch them carefully to make sure they are standing on something sturdy. For example standing on stools is not a good idea. Keep a close eye on students to make sure when you get to this part that there is no horse-play going on to not only distract students but also pose problems with people standing on desk seats. Recommend to the students that a group member stand beside them that they can lean on.
Common Misconceptions on this Topic
A bigger, heavier object falls faster than a smaller, lighter object.
In the absence of air resistance, objects fall with the same acceleration – the acceleration due to gravity. Through this lab, students will see how air resistance alters the acceleration of objects downwards. Through a demo, they will also observe this firsthand as they observe 2 different size balls fall at the same acceleration.
Mass and size has little effect on the air resistance of an object.
Air resistance is dependent on the size and shape of objects. A more massive object will experience less air resistance than a less massive object that is the same size. A larger object experiences more air resistance than a smaller object of the same mass. Students will observe this through their object designs. The designs that take the longest to reach the ground will experience the greatest air resistance.
Inquiry Lab Instructions
Prelab:
1. What does Newton’s second law of motion state?
2. What is friction? What causes it?
If you dropped a bowling ball and a feather from the same height on the Moon, they would both hit the surface at the same time. All objects dropped on Earth are attracted to the ground with the same acceleration. But on Earth, a bowling ball and feather will not hit the ground at the same time. Air resistance slows the feather down.
Question:
How does air resistance affect the acceleration of falling objects?
Materials:
Meterstick Stapler
Masking tape Scissors
Paper Stopwatch
Paper clips
In this lab, you will use the materials above to design something that will maximize air resistance. Below, write your hypothesis for what paper design you think will maximize air resistance. Afterwards, write the step-by-step procedure you will follow to test your hypothesis.
Hypothesis:
Procedure:
Data:
Construct a data table recording the time it takes your design to fall, the distance it fell, and the acceleration of the object as it fell [a = (vf - vt)/t]. Find two other people and test how long it takes their designs to fall the same distance – record the times, distance, and acceleration of the designs on the data table.
Construct a graph displaying the data you recorded in your data table.
Discussion:
1. Compare the falling times of the different designs. Which worked best? What made this design unique?
2. What is the relationship between the falling time and the acceleration of each design?
3. Explain why the designs fell at different speeds.
4. Draw a rough sketch of you dropping your design and label the direction of the force of gravity and the direction of air resistance.
5. Explain how your design maximized the effect of air resistance on your paper’s gravitational acceleration.
6. Infer why a sky diver will fall in spread-eagle position before opening her parachute.
Conclusion:
Was your hypothesis supported? If you could do your experiment again, would you change anything, and if so, what would you change?
Internet Resources
- “Elephant and Feather – Free Fall” (http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/newtlaws/efff.html) shows students an animation of the elephant and feather falling with the same acceleration and includes an explanation of what is happening and a series of true/false questions to check for understanding.
- “Dropping Two Balls Near the Earth's Surface” (http://www.learnerstv.com/animation/animation.php?ani=29&cat=physics) allows you to adjust the horizontal speed of a falling object to show that vertical acceleration is still the same and the objects will reach the ground at the same time.
- “Free Fall: Activities You Can Do At Home” (http://www.nasm.si.edu/exhibitions/gal109/LESSONS/TEXT/FREEFALL.HTM) outlines four activities that can be done at home. It also includes explanations of what each activity illustrated.
- “Air Resistance” (http://www.yteach.com/index.php/resources/air_drag_resistance_area_free_fall_shape_factor_friction_movement_kinetic_static_braking_rolling_force_vector_scalar_quantities_equilibrium_velocity_motion_Newton_mass.html) contains a lesson plan for teaching about air resistance including a whiteboard presentation and six activities.
- “The Science of Baseball” (http://www.exploratorium.edu/baseball/) not only includes several activities to learn the physics behind the game including reinforcing an understanding of projectile motion, but it also includes a historical perspective that students may enjoy as well.
References
- McLaughlin, C. W., Thompson, M., and Zike, D. (2008). Physical Science. New York: The McGraw-Hill Companies.
- Newton's laws of motion (n.d.). Retrieved September 16, 2009 from http://en.wikipedia.org/wiki/ Newton%27s_second_law_of_motion#Newton.27s_second_law:_law_of_acceleration
