Oswego Community Unit School District 308



Newton’s Laws of Gravity and Orbits



Open the Gravity and Orbits simulation. Take 5 minutes to explore how the Earth, Moon, and the Space Station move.

Part 1: Understanding Gravity as a Force

1) Explore the simulation to find out how you can change the force of gravity and observe what happens.

Use different length Gravity Force VECTOR arrows to represent the force of gravity.

2) Draw the Sun’s gravitational pull on the Earth Draw the Earth’s gravitational pull on the Sun

a. In what direction do the arrows point?

b. Gravitational force is always (attractive, repulsive) Circle the correct answer.

c. The star is exerting (more, equal, less) gravity force on the planet, than the planet is exerting on the star.

d. If the Sun and Earth are exerting equal force on each other, why do you think the Earth moves, but the Sun does not move?

Change the variables:

3) Change the MASS of the Star. Draw the force of gravity on each object:

CASE 1 CASE 2

[pic] [pic]

a. Make a statement about the relationship between MASS and the force of gravity:

b. If a gravitational force exists between a very massive object and a less massive object, then the force on

the less massive object will be (greater than, equal to, less than) the force on the more massive object.

4) Change the DISTANCE between the star and the planet by turning on the grid and doubling the distance.

CASE 1 CASE 2

a. As the distance between two masses increase, the gravity force between them (increases, decreases, remains the same) Circle the correct answer.

b. Use the formula to determine the force of gravity if the planet and Sun were:

twice (2) the distance apart _________________g

4 distances apart __________________g

10 distances apart __________________g

5) For the Sun and Earth system:

Select ‘Show the Path’. Push the start button and run the animation. Draw the path of the Earth with Gravity ON and Gravity OFF

GRAVITY ON GRAVITY OFF

a. Describe the path of the planet with gravity off:

b. What role does gravity play in the orbit of an object?

c. What TWO factors affect the strength of gravitational force?

Part 2: Gravity and Motion

6) Select ‘Show the Path’. Check Gravity Force and Velocity. Push the start button and run the animation.

a. Compare the force and velocity vector arrows. In the space below, draw the length of the velocity vector compared to the length of the TWO gravity force vectors.

b. The Gravity force vectors are (greater than, less than, equal to) the velocity vector.

c. Adjust the velocity by sliding the arrow to be smaller and larger. Draw the path of the Earth with less velocity and with more velocity.

LESS VELOCITY MORE VELOCITY

d. What two forces must be equal for an object to remain in orbit?

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e. State Newton’s 3rd Law of Motion: “for every action (force)…….

7) Adjust the MASS of the objects, the DISTANCE between the objects and the VELOCITY of the orbiting object to simulate the following scenarios.

8) Fill in the table to help describe what you find out.

|How can you…. |Explain what you changed |Draw the motion paths |What other changes do you notice?|

|...make the Moon | | | |

|orbit the Earth in a BIGGER | | | |

|circle? | | | |

| | | | |

| | | | |

| | | | |

|...make the Earth | | | |

|Orbit the Sun in more than | | | |

|365 days? | | | |

| | | | |

| | | | |

| | | | |

| | | | |

|...make the Earth | | | |

|take less time to orbit the | | | |

|Sun? | | | |

| | | | |

| | | | |

| | | | |

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| | | | |

|Make the planet have an | | | |

|elliptical orbit around the | | | |

|Sun? | | | |

Part 3: Newton’s 2nd Law



|Test |Location |Acceleration due to Gravity |Object |Mass of Object (kg) |Force on the object (N) |

| | |(m/s2) | | | |

|1 | | | | | |

|2 | | | | | |

|3 | | | | | |

|4 | | | | | |

|5 | | | | | |

|6 |Earth | |Moon | | |

1. Select a location and an object. Select a 2nd location and object.

2. Record the acceleration and mass of each object.

3. Calculate the FORCE of gravity on the objects.

Acceleration = Forcenet \ mass



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Newton’s 2nd Law Problems:

Force = mass x acceleration Acceleration = Force (N) Mass = Force

mass (kg) Accel.

1. A catcher in a professional baseball game exerts a force of 65.0 N to stop the ball. If the baseball has a mass of .145 kg, what is its acceleration as it is being caught?

|Formula |Plug-in numbers |Solve and Units |

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2. What is the mass of an object if a force of 34 N produces an acceleration of 4 m/s2?

|Formula |Plug-in numbers |Solve and Units |

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3. What force must be applied to a 20 kg cart to cause it to accelerate at a rate of 2 m/s2?

|Formula |Plug-in numbers |Solve and Units |

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4. The force of gravity on the moon is much smaller than the force of gravity on Earth for the same object. A bowling ball with a mass of 7.51 kg is pulled downward with a force of 12.2 N.

What is the acceleration of the falling bowling ball on the moon?

|Formula |Plug-in numbers |Solve and Units |

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5. The gravitational force that Earth exerts on the moon equals 2.03x1020 N The moon’s

mass equals 7.35x1022 kg What is the acceleration of the moon due to Earth’s gravitational pull?

|Formula |Plug-in numbers |Solve and Units |

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