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Motion and Forces Chapter 2

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**Force Force- push or pull exerted by one body onto another**

Not all forces are easily recognized Right now several forces are acting on all of us.

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Balanced forces Balanced forces – equal forces act on an object – and cancel each other out If the upthrust (or push up) of the air is equal to the force of gravity (pull down), then the balloon remains suspended in the air.

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Net Force Net force – when one force is greater then another. This is an unbalanced force- and causes an object to accelerate There may be many force directions in any one movement

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Newton Newton’s first law of motion: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force

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Force Force is equal to the mass of the object times the objects acceleration. If any two of these are known the third can be found. F = m x a Mass- kilograms a = m/s2 F = Newtons

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Inertia Inertia = the resistance an object has to a change in its state of motion – objects with greater mass have greater inertia

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**Force is not needed to keep an object in motion.**

Forces accelerate or decelerate objects

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Friction Friction- force that opposes movement between two surfaces that are touching Causes of friction – unsmooth surface, deformations, molecular attraction

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Question Imagine a place in the cosmos far from all gravitational and frictional influences. Suppose that you visit that place (just suppose) and throw a rock. The rock will a. gradually stop. b. continue in motion in the same direction at constant speed.

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**Gravity Gravity is a force that all matter has on all other matter.**

Gravity is affected by mass and distance- As mass increases gravitation increases As distance from the mass increases gravitation decreases

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**↑ Einstein’s Theory of General Relativity**

Newton’s Law of Gravitation

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Gravity Math Near the surface of the Earth gravity accelerates objects at 9.8m/s2 Weight is the force of gravity acting on your body Find weight (Newtons) by multiplying your mass (kg) by acceleration (9.8m/s2) Your mass is the amount of matter in your body. It does not change based on location. Your weight can change depending on the gravitation of your location. i.e. the moon

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