Mr. Bouyer

Day 1 | Lab | Day 4 | Vocabulary Test

Projectile Projectile motion	Orbital motion Escape velocity	Law of Universal Gravitation Weight

Projectile Motion

A rifle is fired horizontally. At the same time, a bullet is dropped from the same height as the rifle barrel. Which bullet hits the ground first?

Projectile: any object thrown in the air.

The path of a projectile has a horizontal component and a vertical component.
• The projectile moves forward because of inertia.
• The projectile accelerates downward because of gravity.

A projectile's path is always a curve.

Find out how bullets fly.

 

Is a projectilefalling?
Shoot two cannonsat each other.
If you can make a jumpshotyou know physics.
Experiment with projectiles.

Your science facilitator has several sets of juggling balls. Learn the juggle a "three ball cascade" during your free time this week.

Test Your Concept Understanding: Answer the question found on this website. Use this website to answer the question: Who first explained the curved path of a projectile? Think about making a catapult out of a mousetrap. Your catapult is to throw a pingpong ball to hit a target about 12 feet away. Make a list of the materials you would need to make it. Make a sketch on a piece of paper of what your mousetrap catapult would look like. Give the drawing and materials list to your teacher.

Days 2 - 3

A person in the back of a pickup traveling 60 miles an hour shoots an arrow streight up in the air. Ignoring air resistance, where does the arrow come down?

Day 4

A rocket is shot into space with a velocity that is less than 25,000 miles an hour. What happens to the rocket?

Johannes Kepler (1571-1630) was a mathematician rather than a scientist. However, he believed the Copernican system and was obsessed with understanding the timing and motion of the celestial bodies. He used Tycho Brahe's data about the motion of Mars in the sky to work out three laws of planetary motion. These laws are the foundation of the science of celestial mechanics.

Kepler's First Law: The orbit of a planet/comet about the Sun is an ellipse with the Sun's center of mass at one focus. Kepler's Second Law: A line joining a planet/comet and the Sun sweeps out equal areas in equal intervals of time. Kepler's Third Law: The squares of the periods of the planets are proportional to the cubes of their semimajor axes. More about Kepler and his laws.

Orbital motion:

An orbiting satellite is a projectile, therefore it has two velocities:
• The satellite has a vertical velocity falling toward the planet.
• The satellite has a horizontal velocity that carries it a horizontal distance that will compensate for the vertical distance it has fallen.

Newton's Principia suggested that if you fire a cannon from a high mountain it could fall, circle the earth, or fly away depending on how hard it was fired.

Fire Newton's Cannon.

Try making a satelliteorbit the Earth.

Escape velocity: the velocity needed to escape the orbital gravity of a planet.

For the Sun - 618 km/sec
For the Earth - 11.2 km/sec or 25,000 mph (about 7 miles per second)
For the Moon - 2.4 km/sec
To calculate escape velocity, use the equation:
• G is the constant 6.67 X 10 ^-4 N m²/ kg²
• M is the mass of the planet
• r is the distance from the satellite to the planet

Careers with NASA

Newton's Law of Universal Gravitation: All objects in the universe attract each other by the force of gravity. The size of the force depends on the mass of the objects and the distance between them. The force of Gravity increases with the mass of an object. Gravitational attraction between objects decreases as the distance between them increases.

Matter is Never Weightless!

But what about astronauts?

• Weight is the measure of the force of gravity on an object.
• Use the following equation to calculate weight:
  Weight = mass X acceleration of gravity

  W = m g

• Mass "m" must be in kilograms. If needed, use this page of conversion factors.
• On Earth, "g" = 9.8 meters/sec² = 22 mph/s.

How much would you weighon another planet?

Homework Assignment 234:
This assignment must be turned in by the beginning of class tomorrow to receive credit.
Scoring criteria

• Given this information:
  • Gravity on the Moon is ¹/₆ that of Earth, making the acceleration of gravity on the Moon 1.6 meters/sec².
  • Major Tom has a mass of 50 kg on Earth.

• Answer these questions:
  1. What is Major Tom's mass on the Moon?
  2. Calculate Major Tom's weight on Earth. (show your calculation)
  3. Calculate Major Tom's weight on the Moon. (show your calculation)

	When everyone at your table has completed the assignment, discuss the following.
	A thought experiment: The curve of the Earth's surface drops about 5 vertical meters for every 8000 meters of horizontal distance. An object dropped near the surface of the Earth will fall about 5 meters in one second. What conditions must be met to throw a baseball around the world?

Research Links:

• Gravitation - Honolulu Community College
• Make Your Own Rocket - Los Alamos National Laboratory
• Orbital Calculations - Hampden-Sydney College Department of Physics and Astronomy
• Kepler's 3 Laws of Planetary Motion - An Interactive Java Program
• Exploring Gravity - An Interactive Java Program
• Target Practice Lab - A High School Physics Lab
• Non-Gunpowder Artillery - Military History Topics

Sample problem answer:
First, convert pounds to kilograms - (200 pounds) (0.45kg/pound) = 90kg
W = mg
W = (90kg) (10m/s²)
W = 900 Newtons

Since all objects fall at the same rate, regardless of their horizontal velocity, both bullets hit the ground at the same time.

Since the arrow and the pickup have the same horizontal velocity, if air resistance is ignored, the arrow should come down in the back of the pickup.

Since the rocket does not reach escape velocity, it will eventually fall back to earth.