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© 2010 Pearson Education, Inc. Making Sense of the Universe: Understanding Motion, Energy, and Gravity
© 2010 Pearson Education, Inc. How do we describe motion? Precise definitions to describe motion: Speed: Rate at which object moves Example: 10 m/s Velocity: Speed and direction Example: 10 m/s, due east Acceleration: Any change in velocity units of speed/time (m/s 2 )
© 2010 Pearson Education, Inc. The Acceleration of Gravity All falling objects accelerate at the same rate (not counting friction of air resistance). On Earth, g 10 m/s 2 : speed increases 10 m/s with each second of falling.
© 2010 Pearson Education, Inc. The Acceleration of Gravity (g) Galileo showed that g is the same for all falling objects, regardless of their mass. Apollo 15 demonstration
© 2010 Pearson Education, Inc. Momentum and Force Momentum = mass velocity A net force changes momentum, which generally means an acceleration (change in velocity). Rotational momentum of a spinning or orbiting object is known as angular momentum.
© 2010 Pearson Education, Inc. How is mass different from weight? Mass – the amount of matter in an object Weight – the force that acts upon an object You are weightless in free-fall!
© 2010 Pearson Education, Inc. There is gravity in space. Weightlessness is due to a constant state of free-fall. Why are astronauts weightless in space?
© 2010 Pearson Education, Inc. Realized the same physical laws that operate on Earth also operate in the heavens one universe Discovered laws of motion and gravity Much more: experiments with light, first reflecting telescope, calculus… Sir Isaac Newton (1642–1727) How did Newton change our view of the universe?
© 2010 Pearson Education, Inc. What are Newtons three laws of motion? Newtons first law of motion: An object moves at constant velocity unless a net force acts to change its speed or direction.
© 2010 Pearson Education, Inc. Newtons second law of motion: Force = mass acceleration
© 2010 Pearson Education, Inc. Newtons third law of motion: For every force, there is always an equal and opposite reaction force.
© 2010 Pearson Education, Inc. Gravitational Potential Energy On Earth, depends on: –objects mass (m) –strength of gravity (g) –distance object could potentially fall
© 2010 Pearson Education, Inc. Gravitational Potential Energy In space, an object or gas cloud has more gravitational energy when it is spread out than when it contracts. A contracting cloud converts gravitational potential energy to thermal energy.
© 2010 Pearson Education, Inc. What determines the strength of gravity? The universal law of gravitation: 1.Every mass attracts every other mass. 2.Attraction is directly proportional to the product of their masses. 3.Attraction is inversely proportional to the square of the distance between their centers.
© 2010 Pearson Education, Inc. Kepler first tried to match Tychos observations with circular orbits But an 8-arcminute discrepancy led him eventually to ellipses. If I had believed that we could ignore these eight minutes [of arc], I would have patched up my hypothesis accordingly. But, since it was not permissible to ignore, those eight minutes pointed the road to a complete reformation in astronomy. Johannes Kepler ( ) Kepler and the Laws of Planetary Motion
© 2010 Pearson Education, Inc. An ellipse looks like an elongated circle. What is an ellipse?
© 2010 Pearson Education, Inc. Keplers First Law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus. What are Keplers three laws of planetary motion?
© 2010 Pearson Education, Inc. Keplers Second Law: As a planet moves around its orbit, it sweeps out equal areas in equal times. This means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.
© 2010 Pearson Education, Inc. More distant planets orbit the Sun at slower average speeds, obeying the relationship p 2 = a 3 p = orbital period in years a = avg. distance from Sun in AU Keplers Third Law
© 2010 Pearson Education, Inc. How does Newtons law of gravity extend Keplers laws? Ellipses are not the only orbital paths. Orbits can be: –bound (ellipses) –unbound parabola hyperbola Keplers first two laws apply to all orbiting objects, not just planets.
© 2010 Pearson Education, Inc. Center of Mass Because of momentum conservation, orbiting objects orbit around their center of mass.
© 2010 Pearson Education, Inc. Newton and Keplers Third Law Newtons laws of gravity and motion showed that the relationship between the orbital period and average orbital distance of a system tells us the total mass of the system. Examples: Earths orbital period (1 year) and average distance (1 AU) tell us the Suns mass. Orbital period and distance of a satellite from Earth tell us Earths mass. Orbital period and distance of a moon of Jupiter tell us Jupiters mass.
© 2010 Pearson Education, Inc. Newtons Version of Keplers Third Law p = orbital period a = average orbital distance (between centers) (M 1 + M 2 ) = sum of object masses
© 2010 Pearson Education, Inc. How do gravity and energy together allow us to understand orbits? Total orbital energy (gravitational + kinetic) stays constant if there is no external force. Orbits cannot change spontaneously. Total orbital energy stays constant.
© 2010 Pearson Education, Inc. So what can make an object gain or lose orbital energy? Friction or atmospheric drag A gravitational encounter Changing an Orbit
© 2010 Pearson Education, Inc. If an object gains enough orbital energy, it may escape (change from a bound to unbound orbit). Escape velocity from Earth 11 km/s from sea level (about 40,000 km/hr) Escape Velocity
© 2010 Pearson Education, Inc. How does gravity cause tides? Moons gravity pulls harder on near side of Earth than on far side. Difference in Moons gravitational pull stretches Earth.
© 2010 Pearson Education, Inc. Tides and Phases Size of tides depends on phase of Moon.
© 2010 Pearson Education, Inc. Tidal Friction Tidal friction gradually slows Earths rotation (and makes the Moon get farther from Earth). The Moon once orbited faster (or slower); tidal friction caused it to lock in synchronous rotation.
© 2010 Pearson Education, Inc. Why do all objects fall at the same rate? The gravitational acceleration of an object like a rock does not depend on its mass because M rock in the equation for acceleration cancels M rock in the equation for gravitational force. This coincidence was not understood until Einsteins general theory of relativity.
© 2010 Pearson Education, Inc. Just the Start! Tidal Forces around Condensed Objects –Neutron Star by Larry Niven Orbital Mechanics –Hohmann Transfer Orbits, etc. –Nice website: terrific-resources-for-writing-space-based-hard- science-fiction/ that included a great page on orbital mechanics, as well as other stuff (exoplanet links, a plug for Stan & Analog, etc.). terrific-resources-for-writing-space-based-hard- science-fiction/
Motion of an object travelling at constant speed in a circle Lets explore the kinematics of circular motion. Why is it accelerating, if the speed is constant?
Kepler’s Laws. Kepler and the Physics of Planetary Motion Laws of Planetary Motion Law 1 - Law of Ellipses Law 2 - Law of Equal Areas Law 3 - Harmonic.
Chapter 3 Force, Mass and Acceleration Newton’s Laws.
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13 Universal Gravitation Everything pulls on everything else.
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Gravity Don’t Let It Get You Down! The Truth About Gravity u Gravity is a phenomenon u The phenomenon results in a force which can accelerate objects.
Chapter 8 Motion and Forces. Reference Frame Clues are often given by looking at other objects in your surroundings Clues are often given by looking at.
SPS8. Students will determine relationships among force, mass and motion b. Apply Newton’s three laws to everyday situations by explaining the following:
Section 2: Newtons Law of Gravitation In 1686 Isaac Newton published his Universal Law of Gravitation. This explained gravity as a force of attraction.
Chapter 13 Gravitation PhysicsI Newtons law of gravitation Besides the three laws of motion, Newton also discovered the universal law of gravitation.
© 2005 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their.
Newton’s Law of Universal Gravitation Nicolaus Copernicus- Polish astronomer who said that the Earth revolves around the sun, not the other way around!
CH 3—Forces. Force, Mass, and Acceleration For any object, the greater the force is that’s applied to it, the greater its acceleration will be. The acceleration.
Forces and Motion 2 2 Force A force is a push or a pull that one object exerts on another object. Objects like floors, chairs, and Earth also exert forces.
Movement. Movement The amount of change in movement of an object is based on the mass of the object and the amount of force exerted.
Chapter: Forces and Changes in Motion Table of Contents Section 3: The Laws of MotionThe Laws of Motion Section 1: Motion Section 2: Forces and MotionForces.
More Light, History, Gravity, Distance, Relativity, and Space-time.
Chapter 12 - Forces 1- Newtons First and Second Laws 2- Gravity 3 - Newtons Third Law.
Gravity Dont Let It Get You Down! The Truth About Gravity u Gravity is a phenomenon and results in a force which can accelerate objects with mass. u.
Warm-up: Anticipation Guide Directions: Carefully read the statements on your anticipation guide. Think about the statement and determine if you generally.
Laws of Motion. Newton s First Law an object at rest remains at rest and an object in motion maintains its velocity (stays in motion) unless it experiences.
Newtons Laws of Motion Forces. Newtons First Law of Motion What happens to a ball rolling along the ground? What happens to a ball rolling along the ground?
Topic 2: Motion and Force Dynamics By: Mrs. Fagan.
Forces & Newton’s Laws of Motion. Sir Isaac Newton ( ) English scientist and mathematician famous for his discovery of the law of gravity and.
Stop Faking It! Force & Motion. Newtons First Law of Motion n Objects in motion tend to stay in motion until something hits them n Objects at rest tend.
§A. A polish astronomer in the 16th Century, realized that our model of our solar system worked much better if we put the Sun at the center and not.
Distance: describes how far an object has moved, regardless of its direction ex: 40km east + 25km west = 65 total km traveled Displacement: describes.
Gravity Unit F, Chapter 1, Section 1 pF6-11. Forces Make Things Move Force: push or pull – Act of objects – Often affect motion of objects Cause objects.
How Can You Describe Motion? Chapter 1, Lesson 2; pF14-21.
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