Newton’s Laws of Motion



Newton’s Laws of Motion

I. Newton’s 1st Law of Motion - Inertia

• Law states that an object at rest will stay at rest, or an object in motion will stay in motion unless a force acts upon it

o What does it mean by a force?

▪ A push or pull in a specific direction

• examples: gravity, magnetism, air, friction

▪ contact force - force touches object

▪ non-contact force - force does not touch object

o What is a balanced force?

▪ a force that is equal in strength and opposite in direction

▪ they cancel each other out so the force = 0 Newtons

▪ results in no motion

o What is an unbalanced force?

▪ a force that is unequal and moves towards the stronger force

▪ if the forces (arrows) are going in the same direction ( add the forces together

▪ if the forces are going in different directions ( subtract the forces

o We use a vector (or an arrow) to show the direction and strength of a force

▪ the longer the arrow, the stronger the force

▪ the shorter the arrow, the weaker the force

• Other things to know about Inertia

o What is a mass?

▪ the amount of “stuff” or matter in an object

▪ more mass = more inertia

▪ less mass = less inertia

II. Newton’s 2nd Law of Motion

• F = ma (force = mass x acceleration)

o units for each

▪ force - Newton (N)

▪ mass - kilograms (kg) or grams (g)

▪ acceleration - meters per second squared (m/s2)

o Using the F=ma formula

▪ Solving for Force

• F = ma mass times acceleration

• answer is in Newtons (N)

▪ Solving for mass

• m = F / a force divided by acceleration

• answer is in kilograms (kg)

▪ Solving for acceleration

• a = F / m force divided by mass

• answer is in meters per second squared (m/s2)

• Other things to know about Newton’s 2nd Law

o Mass vs. weight

▪ mass always stays the same

▪ weight changes with gravity

▪ weight is the force of gravity on an object

▪ more mass = more gravity

▪ more distance = less gravity

o acceleration

▪ acceleration to Earth due to gravity is always 9.8 m/s2

III. Newton’s 3rd Law of Motion

• Law states that for every action, there is an equal and opposite reaction

o examples: walking, kicking your foot back to make the skateboard to move forward, swimming, a bird flapping its wings to make it fly, the space shuttle taking off

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