Exploring Newtons’ Second Law using Simulations



Exploring Newtons’ Second Law using a Simulations

Name:

Background:

Newtons second law states that when a force acts upon an object, it will cause the object to accelerate.

The greater the force the greater the acceleration.

The simulation the website allows you to explore the relationship between force, mass and acceleration. The simulation allows to select different objects (each with a different mass) to which a horizontal force can be applied (by a fellow named Joe). Different aspects of the objects motion can then be measured.

Activity 1: Explore the Sim

A screenshot of the simulation is shown below.

[pic]

Spend 5 minutes exploring the sim. Find out the following:

How do you select an object? How do you change the mass of the object?

How do you apply a push? How do you change the force of the push?

How do you determine the total (net) force being applied to the object?

Can you turn the free body diagram on?

How can you find out about the motion of the object?

Can you quantify the acceleration of the object?

Can you turn friction off?

How do you ‘reset’ the sim?

What other settings can you change? Should these be changed?

Are you able to record your experiments so you can review what happened?

Use this space to make notes about the sim

Activity 2: Explore the effect of force on acceleration (with no friction)

Now you have had a chance to explore the sim, let’s see if you can figure out the relationship between the total force applied and the acceleration of an object.

Prediction: What effect will increasing the force have on the acceleration of an object?

Start by turning friction off.

Select an object for Joe to push.

Record the mass of the object.

Have Joe push the object with different magnitudes of force, record the acceleration of the object for each force.

Calculate the quotient of force and mass (force ÷ mass)

|Table 1: Activity 2 Results |

|Mass of object (kg) |Total force (N) |Acceleration (m/s2) |[pic] |

|Keep this constant | | | |

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What did you notice about the magnitude of acceleration and the quotient of force and mass?

Try and write a rule to describe the relationship between force mass and acceleration.

Activity 3: Explore the effect of force on acceleration (with friction)

Repeat the experiment from activity 2, but this time have friction turned on.

Will you be able to use the rule you developed in activity 2?

How will adding friction change your results?

|Table 2: Activity 3 Results |

|Mass of object (kg) |Total force (N) |Acceleration (m/s2) |[pic] |

|Keep this constant | | | |

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How did your results from activity 3 compare to your results from activity 2?

Can you explain the relationship between the force applied to an object, the mass of an object and the acceleration of the object.

Activity 4: Using what you have learned·

Now let’s see if you can apply what you have learned. Some of the cells in the table below have been left blank. Predict what the answer should be, then use the simulation to find out if you were correct.

Total Force (N) |Mass (kg) |Acceleration (m/s2) | |Predicted answer |Simulation answer | |200 |10 |? | | |

| |500 |20 |? | | |

| |? |50 |10 | | |

| |? |100 |15 | | |

| |250 |? |5 | | |

| |1000 |? |20 | | |

| |? |150 |15 | | |

| |? |250 |25 | | |

| |

And finally ......

What do you now understand about the relationship between Force, Mass and Acceleration?

Gravity, Orbits and Kepler’s Laws

LEARNING OBJECTIVES

• To learn how the shape and period of a planet orbiting a star depend on the mass of the star and the mass of the planet

• To learn how the shape of the orbit depends on the speed and orbital radius of the planet.

• To observe Kepler’s laws

INTRODUCTION

Planets or other objects orbiting a star are accelerating -- they are continually changing direction. The force that produces this acceleration is the gravitational attraction to the star. In this activity we will use a simulation to observe and learn about these orbits and relate them to Kepler’s laws.

[pic]

PROCEDURE

Go to the website again and click on the “Gravity and Orbits” simulation.

Use the “Model” tab. The settings on the right should be for Earth and Our Sun. Begin the activity with original values. Hit Reset if they’ve shifted. Click on: Gravity Force, Velocity, Path and Grid.

Follow all the procedures described below. Write answers on this sheet. Answers need to be in complete sentences with proper capitalization.

1. Note that the blue force arrow on Earth is the same size as the blue force arrow on the Sun. Why is this so? What law(s) is (are) being illustrated?

2. Hit the start arrow and observe the path.

2a. Describe the shape of the orbit.

2b. Which of Kepler’s laws did this illustrate? (State the law – don’t simply give the number of the law.)

2c. Measure the time for one period of revolution. (You may have to practice stopping at “one period” and you may want to slow the Sim speed.)3. Slide the “Planet” selector to the left. You will be maintaining the distance to the Sun but replacing Earth with a planet having a smaller mass.

3a. Before hitting start, what changes do you notice? Why do think things changed?

3b. Hit start and carefully observe the orbit and determine the period. Write down your observations.

RESET

4. Slide the “Planet” selector to the right – maintaining the distance to the Sun but replacing Earth with a planet with a larger mass.

4a. Before hitting start, what changes do you notice? Why do think things changed? What law(s) is being illustrated?

4b. Hit start and carefully observe the orbit and determine the period.

4c.What do you learn from your measurements in parts 2,3 and 4?

RESET

Slide the “star” tab one notch to the right, thus replacing the Sun with a star of greater mass.

5a. Before hitting start, what changes do you notice?

• Why do think things changed?

• What law(s) is being illustrated?

5b. Hit start and carefully observe the orbit and determine the period.

5c. Carefully observe the speed (the length of the velocity arrow). Describe what you observe about the speed at different locations in the orbit. Which of Kepler’s laws did this illustrate? (State the law – don’t simply give the number of the law.)

5d. Carefully observe the force vector. Describe what you observe about the force at different locations in the orbit. Why do you think the force changes? Which of Newton’s laws did this illustrate?

In conclusion…

Summarize what you learned from this activity by:

a. listing the key scientific terms encountered in the activity.

b. constructing a bulleted list that utilizes these key words (and, as needed, words from previous activities) in summarizing what you learned.

Additional Questions

1. T/F explain your choice based on your observations in this activity: Earth is accelerating

.

2. Earth exerts a gravitational force on the Sun and the Sun exerts a gravitational force on Earth.

a. Which exerts the larger force? Explain your choice.

b. Which has the greater acceleration? Explain your choice.

3. Imagine another solar system with a star of the same mass as the Sun. In this solar system there is a planet with a mass twice that of Earth orbiting at a distance of 1 AU from the star. What is the orbital period of that planet? Explain your answer based on what you observed in this activity.

4. T/F explain your choice based on your observations in this activity:

Doubling the mass of the Sun would have no effect on the period of Earth.

5. As a planet orbits the Sun in an ellipse, at what point on the ellipse is the Sun’s gravitational force on it greatest? Explain your reasoning. At what point is the acceleration the greatest? Explain.

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