Chapter 5 Gravity and Motion

Essential Question How are forces related to motion

Force and motion before Newton Kepler explained the motion of the planets but not the why they move People needed a better understanding of motion, phase one slow progress towards understanding – phase two Newton solves the problem

Galileo’s Experiments First to attempt experimental physics or do experiments instead of just observe The impetus theory – developed in the 14 th century – objects moved as long as force was applied They needed to be explainable through mathematics – to remove false or bad common knowledge

Galileo’s Experiments He used two different massed objects to roll down a ramp – No matter the weight they accelerate at the same speed Determined what caused the difference in dropping objects was the effect of air resistance Was the first to use accurate clocks in his experiments Motion was consistent and would continue unless an outside force stopped it – air resistance, friction or drag of water

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Descartes and Inertial motion Rene Descartes (1596 – 1650) French Philosopher Inertial motion – an object in motion will stay in motion at the speed and direction Believed that all changes in motion resulted in a collision with particles Eliminated the concept of perfect circular motion

Planetary Motion before Newton The rotation of the crystalline shells caused the movement of all shells like a clock The concept of shells was dismissed by Copernicus and others, but none had explain how the solar system moved Kepler’s discoveries suggested an external force that caused this motion

Kepler’s Explanation Kepler stated that there were rays that came off the sun, rotated with the sun and these would push the planets in there orbits The change in orbital speed was due to magnetic fields – the planets would be pulled toward the sun or pushed away The sun’s south pole was at the center of the sun and the north on the surface. Our tilted axes would allow the speed up and slow down

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Robert Hooke Robert Hooke (1653 – 1703) contemporary of Newton (1642 – 1727) Proved that a central force could lead to a orbital motion Proposed that gravity has the cause of the central force Was not able to determine the change in gravity over distance

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Isaac Newton Made most of his early discoveries while living on his family farm – optics, universal gravity, differential and integral calculus Needed a challenge to publish his discoveries – took 20 years to publish his work on planetary motion

Essential Questions What are momentum and angular momentum What do they have to do with motion and the orbits of the planets

The Law of Inertia An object remains at rest or continues in motion at constant velocity unless it is acted on by an unbalanced external force Velocity describes the speed and direction of an object – a change in speed or direction is a change in velocity Acceleration is the rate at which velocity changes Mass is the resistance of an object to acceleration Momentum is constant unless the object is affected by an outside force ( same speed, direction and vector)

The Law of Force It is some sort of push or pull. “When a net force act on an object, it produces a change in the momentum of the object in the direction which the force acts” A force can be detected by observing a change in motion Both mass and velocity will determine the momentum of a body Acceleration only occurs when there is an unbalanced force F= MA

The law of Action and Reaction Newton’s third law – when one body exerts a force on a second body, the second body also exerts a force on the first. These are equal in strength, but opposite in direction This is also known as equal and opposite, think of a pool table The mass of an object is a factor in the reaction

Centripetal acceleration Is a force that pulls an object to the center, diverting it from its straight path This was first mathematically described by Christian Huygens in 1673 (Newton solved it in 1666) Found that orbital speed of planets is connected to the distance from the center force

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The Law of Gravitation That every two particles in the universe attach each other Link 32 feet per second second Weight and Mass of objects Weight is a measure of how hard gravity is pulling on an object Mass is always constant.

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Essential Question

Essential Questions