ASTRO .docx - ASTRO 01 UNIT 1 Gravity Newtons Laws of...

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ASTRO 01 UNIT 1 Gravity Newton’s Laws of Motion 1.) First law: An object at rest, or in motion in a straight line at a constant speed, will remain in that state unless acted upon by a force. o First Law describes inertia — the tendency of an object at rest to remain at rest, or of a moving object to continue moving. When one applies a force to an object, it causes the object to accelerate (the Second Law), which may be a deceleration (negative acceleration) depending on the direction in which the force is applied. In addition to causing acceleration (positive or negative), an applied force may alter the direction of motion of the target object. o Something that isn’t moving won’t move unless something else makes it/ applies force 2.) Second Law: The acceleration of a body due to a force will be in the same direction as the force, with a magnitude inversely proportional to its mass.Or: the magnitude of force necessary to produce a certain acceleration on a body will be directly proportional to its mass — a higher mass requires greater force.(This is usually written as F = ma, or Force = mass x acceleration). 3.) Third Law: For every action, there is an equal and opposite reaction. o The Third Law describes the situation of "push on something, and the something pushes back." An example is a person jumping — one essentially kicks downward, exerting a force in a downward direction, yet the surface below the feet stays more-or-less still and the end effect is to propel the jumper upwards. Even a person standing still on the ground is experiencing a force ( gravity ) that would accelerate the person downward, if not for the ground (and the person's legs) exerting an opposite force upward. Newton's Law of Universal Gravitation All objects with mass experience attraction towards each other as a result of the gravitational force between them. The strength of this force between two objects is given by G ( m 1 m 2 ) F g = ————————— r 2 Where... F g is the force of gravity G is the universal constant of gravitation m 1 is the mass of one object m 2 is the mass of a second object r is the distance between the two objects The gravitational force is then directly proportional to the mass of each interacting object (or to the product of them), and inversely proportional to the distance between them, squared.
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Recall from Newton's Laws that F = m a where ' a ' is the acceleration; if the force ' F ' is due to gravity, the ' a ' may be written as ' g ' ( F = m g ) If, say, the first mass is you , and the second mass is the planet you are standing on, then the gravitational acceleration you experience is directly proportional to the mass of the planet, and inversely proportional to the square of its radius; i.e.
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