Activity4.2.2 Newton’s Laws of Motion

Introduction

Aerospace design engineers use aerodynamics, the science of motion of air and forces acting on bodies in air, to design airplanes that will fly. One of the jobs of an aerospace engineer is to create wing shapes that produce lift as the air moves over the wings. If an airplane is going to fly, the amount of lift must be greater than the force of gravity, and the amount of thrust produced by the engine must be greater than the drag force created by air resistance. Wing shapes that provide lift and have the proper angle of attack (the angle at which a wing meets the flow of air) can then help an airplane overcome gravity. Research has shown that a wing with a streamlined shape can overcome drag with the thrust of engines. The less drag on an airplane, the less power it needs to move.

In this activity you will learn the basic concepts of aerodynamics, including basic definitions, Newton’s laws of motion, and forces acting on an airplane during flight, and in the next activity, Bernoulli’s principle, which is the major contributor to lift. Knowledge of these science concepts will help you as you investigate atmospheric flight later in this unit.

Procedure

Answer the questions below as your teacher guides you through several activities.

Discovery of Forces – Newton’s First Law

Watch your teacher’s demonstration to answer the question below.

  1. Read the statement below and explain why you agree or disagree with the statement. Give an example.

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Changes in Force – Newton’s Second Law

Think about riding a skateboard. If you push off lightly, will you travel very far? What if you push off harder? When you push off, you are applying a force to an object with mass (that would be you), and when you put yourself into motion, you are accelerating. Think about this while completing the following experiment.

Several students will time how long it takes for a dragster to travel the length of the track when different forces are applied to the dragster. Read all directions before you begin.

  1. Make a prediction in the space below on how you think a dragster will accelerate down the track using different amounts of force. Use the supplied data table to record your information.
  1. Your instructor will set a dragster on the track and tell you the mass of the dragster. Record the mass in the correct location in the data table.
  2. We will run the dragster a total of 9 times – 3 times at each specified amount of force. Your instructor will set the force levels on the compressor.
  • 3 runs with a force of 40 psi
  • 3 runs with a force of 60 psi
  • 3 runs with a force of 80 psi
  1. Record the timeanddistance traveledfor each run. Note: the run time is the time from the launch (3-2-1-LAUNCH!) until the dragster hits the end of the track or comes to a complete stop.
  2. Use your data to calculate the average velocity (speed) of the dragster for each force used. Speed = distance ÷ time
  3. Use the calculated velocity (speed) and the time to determine the acceleration. Acceleration = velocity ÷ time

Technically, acceleration is defined as the change in velocity divided by the change in time. Acceleration = (final velocity - starting velocity) ÷ (final time - starting time) However, since our starting velocity and starting time are both zero, we are able to shorten the equation as shown above.

  1. Complete the data table for changes in force.

Mass of the dragster ______grams

Force / Distance / Time / Average Velocity (distance/time) / Acceleration (velocity /time) / Average Acceleration
40 psi
40 psi
40 psi
60 psi
60 psi
60 psi
80 psi
80 psi
80 psi

Changes in Mass – Newton’s Second Law

Think about pushing a shopping cart. When the cart is empty, it is easy to start moving, easy to keep moving, and easy to stop. However, when the cart is full, it becomes much more difficult to start and stop. Keep this in mind as you complete the following lab.

  1. Make a prediction in the space below regarding how you think dragsters of different masses will accelerate down the track if the amount of force stays the same.
  1. Use the supplied data table to record your information.
  2. Your instructor will set a dragster on the track and tell you the force being used. Record the force in the correct location in the data table.
  3. We will run the dragster 9 times – 3 times with each dragster of a different mass. Your instructor will set the force levels on the compressor.
  4. Record the timeand distance traveledfor each run. Note: the run time is the time from the launch (3-2-1-LAUNCH!) until the dragster hits the end of the track or comes to a complete stop.
  5. Use your data to calculate the average velocity (speed) of the dragster for each force used. Speed = distance ÷ time
  6. Use the calculated velocity (speed) and the time to determine the acceleration. Acceleration = velocity ÷ time

Technically, acceleration is defined as the change in velocity divided by the change in time. Acceleration = (final velocity - starting velocity) ÷ (final time - starting time) However, since our starting velocity and starting time are both zero, we are able to shorten the equation as shown above.

  1. Complete the data table for changes in mass.

Constant air pressure: ______psi

Mass / Distance / Time / Average Velocity (distance/time) / Acceleration (velocity /time) / Average Acceleration

Conclusions

  1. If the mass remains constant and the force changes, what happens to the acceleration?
  1. If the force remains constant and the mass changes, what happens to the acceleration?
  1. Were some of your results inconsistent with the rest of the data? If so, why do you think the experiment produced unexpected results?
  1. Newton’s second law says that force and acceleration are directly proportional, meaning that if the force is increased three times, the acceleration should increase three times. Did this occur in your lab? If not, why do you think it didn’t happen?
  1. What effect does resistance have on the acceleration of the dragsters? Be sure to discuss both air and friction.
  1. Read the statement below and explain why you agree or disagree with the statement. Give an example.

Acceleration is produced when a force acts on a mass. The greater the mass of the object being accelerated, the greater the amount of force needed to accelerate the object. Therefore, Force = mass x acceleration or F = ma.

Reaction of Forces – Newton’s Laws

Newton’s third law states that

For every action there is an equal and opposite reaction.

This means that for every force, a reaction force exists that is equal in size but opposite in direction. Whenever an object pushes another object, it gets pushed back in the opposite direction equally.

For this activity you will simulate launching a bottle rocket. You will determine the optimum amount of water for maximum rocket height.

Compressed air is air stored at a higher pressure than atmospheric pressure. Energy contained in compressed air is called potential energy because it is energy that is available for use. It has the potential to be turned into action energy, also called kinetic energy. Once all of the potential energy is used up (meaning the air has reduced in pressure to that of the unconfined surrounding air), the air will not push anymore. Think about how this may apply in the activity you are about to complete.

Let’s investigate the relationship between the amount of water in the bottle and the distance that a rocket can fly.

  1. Individually use the following website to simulate a water rocket:
  1. Make a prediction on the effect the amount of water in the bottle has on the distance the rocket will travel.
  1. Run the simulation software using the 2 liter bottle. You may choose to either use or omit the nose cone, but once you make the decision, you must run all of the tests the same way (with or without the nose cone).
  2. Changing only the amount of water in the rocket, run the simulation five times and record the data in the table below.

Trial / % Water in the Bottle / Meters Traveled / Maximum Velocity
1
2
3
4
5

Conclusions

  1. Restate your prediction. Did the test data support your prediction? If so, explain how. If not, give possible reasons why not.
  1. Would the use of compressed air and water be practical in lifting rockets into outer space? Why or why not?

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GTT–Unit 4– Lesson 2–Activity4.2.2 – Newton’s Laws of Motion– Page 1