Newton’s Laws A Summary

  English mathematician, physicist, astronomer.  Born the same year Galileo died  Began to prove Galileo’s theories through math. Isaac Newton

Newton’s First “Every object persists in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.” ---Isaac Newton’s original wording. In other words: “An object in motion will stay in motion until acted on by an outside force, and an object at rest will stay at rest until acted on by an outside force.”

Newton’s First Became known as the Law of Inertia Put simply: – The Law of Inertia is an objects tendency to resist changes in motion – Related to mass The more mass an object has, the more inertia it has.

Newton’s First Newton’s first law deals with objects at rest or objects moving at a constant velocity. In both of these cases, no (net) force is on the object.

His Law Explains Why you eventually come to a stop when you are driving down the road and you take your foot of the gas and brake. – So why do you? Why a ball at the top of the hill will start rolling down without being pushed. – Why does it? Can you think of a situation in which something either starts moving without an outside force or stops moving without an outside force?

Newton’s Second Law (The Easy One) Basically: F=ma – Mass and acceleration are directly proportional to the Force applied. More mass requires more force to overcome the inertia (state of resting or moving). More acceleration requires more force.

Newton’s Second There are inverse relationships as well m=F/a mass is inversely proportional to acceleration. Meaning: If the Force remains constant; as you raise the mass the acceleration will go down. Then there’s: a=F/m Acceleration is inversely proportional to mass. Meaning: If the Force remains constant; as you increase the acceleration you decrease the mass.

Newton’s Second Law Newton’s second law deals with objects that are accelerating, or changing their velocity. In this case, there must be a net force on the object.

Before the Third, Recall the First Recall from Newton’s First Law – All objects have inertia- the more massive the object, the more inertia it has. – Inertia is the resistance to change in state of motion. So if an object is at rest, it wants to stay at rest. If an object is in motion, it wants to stay in motion. – The more mass an object has, the more inertia it has, so the more it will resist these changes in motion.

And the Second “The larger the force acting on an object, the greater the acceleration of the object. The greater the mass of the object, the less the acceleration of the object.” In equation form: m=F/a or a= F/m or F=ma

Newton’s Third Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. or To every force there is an equal and opposite force.

Example

Newton’s Laws That was what ruled the universe for close to two centuries Until………………………….

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Mass, weight, support force

Mass Plainly put, mass is the amount of “stuff, ” or matter in an object. We can also think of it as a measure of an object’s inertia.

Weight Weight is a measure of how hard gravity is pulling on an object. If you imagine a scale as having a spring inside it, between you and the earth, then the harder the earth pulls the more this spring will compress. This translates (on the scale) to more weight.

Question: If you go to the moon, where the force of gravity is 1/6 that of earth’s, does your mass change?

Answer: No. Travelling anywhere does not change your mass, as your mass is the measure of how much stuff you are made out of, and that does not change simply by putting you in a different place.

Question: If you travel to the moon, where gravity is 1/6 that of earth’s, does your weight change?

Answer Yes. If the gravity is less, you will weigh less. Think about it: If you are standing on that scale, you will compress it less if gravity is not pulling as hard, and therefore it will read less.

So what is the relationship between mass and weight? The weight of an object is equal to the objects mass multiplied by the acceleration of gravity, or: w= mg where g = 9.8 m/s 2 (on earth)

Weight and mass, cont. So if your textbook has a mass of 1kg, it has a weight of: w = (1kg)x(9.8 m/s 2 )= 9.8 kgm/s 2 = 9.8 N Notice that the units for weight is Newtons, also the units for force. This makes sense!!! Remember, weight is a measure of the force of gravity acting on an object, or how hard gravity is pulling on an object.

Your weight? Let’s say you have a mass of 65 kg. How much do you weigh? W= mg = (65 kg)x(9.8 m/s 2 ) = ? N So the earth’s gravity is pulling on you with a force of 637 N. What if you were on the moon (g moon = 1/6 th Earth, g moon = ?), How much would you weigh? W= mg = (65kg) x (1.67 m/s 2 ) = ? N W = 109N (notice that your weight on the moon changes but not your mass)

And in outer space, where there is no gravity? How much do you weigh? W= mg = (65kg)x(0) = 0 (weightlessness) (but you still have mass)