Newton’s Laws of Motion Isaac Newton (1642 – 1727)

What is a Force? Force can be defined as a or anything else that has the ability to change motion. or a

In SI units, a force is measured in newtons (N). One newton is about the amount of force it takes to lift a quarter-pound cheeseburger.

How do you figure force? Force = mass x acceleration Newton (N) (kg) ( m/s 2 ) Easier than saying kilogram  m/sec 2 F = m a

To Understand Force… You must understand the difference between AND 2 Kg Mass

Mass What is Mass? 1 Kg Mass 2 Kg Mass 1.5 Kg Mass The amount of “matter” in an object. Mass is measured in k kk kilograms.

How is Mass Different Than Weight? 1.0 Kg Mass 9.8 N 1.5 Kg Mass 14.8 N 2.0 Kg Mass 19.7 N Weight is mass times the force of gravity Weight is a measurement of FORCE. How can you measure force? Calculate mass x acceleration. (1 kg x 9.86 m/s 2 ) F=ma (1.5 kg x 9.8 6m/s 2 ) (2 kg x 9.86 m/s 2 ) Acceleration due to gravity (9.8 m/s 2 )

Kg Mass is 220 lbs On the sun 220 lbs. would weigh 5,956 lbs. On Mars 220 lbs. would weigh 82.9 lbs. On the moon 220 lbs. would weigh 35 lbs. Being pulled by different gravity? Your weight may be different. However, your mass never changes. What’s “Your Weight On Other Worlds?”

Let’s look at Newton's three laws of motion... These laws explain why objects move (or don't move). Isaac Newton is the first scientist responsible for formulating laws regarding motion.

An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration For every action force there is an equal and opposite reaction force.

Newton’s First Law: Balanced Forces Stay at rest: a book on a table Stay in motion: a bowling ball tossed in space Inertia An object will maintain a constant state of motion. (Speed and direction remain unchanged) This means an object at rest tends to stay at rest and an object in motion continues in the same direction with the same speed. It will go on and on forever. This is known as Science Table pushes up on book Gravity pulls down on book Balanced Forces

Newton’s First Law: Unbalanced Forces The book below slides and then stops because of a resistant force called friction. Friction is force that opposes motion. In space there is no resistance to cause friction, so a bowling ball would stay in motion… unless another object got in the way An unbalanced force is a force that changes the motion. Science Force of friction stops the book

What causes friction? There are two factors which affect friction between two surfaces: –Kind of surfaces in contact (rough or smooth) –Amount of force pressing the surfaces together The rougher the surface and the stronger the force between the surfaces, the greater the amount of friction.

Of course “frictional” force happens on earth... but, if you weren’t wearing a safety belt you would continue your motion… Don’t let this happen to you! BUCKLE UP!!!!

There are 4 types of friction 1) Static friction: friction between two surfaces which are not moving past each other Example: trying to move a box and it will not move

There are 4 types of friction 2) Sliding friction: occurs when a force is great enough to overcome the static friction Example: two people create enough force to make the box move

There are 4 types of friction 3) Rolling friction: the friction which enables wheels to turn and objects to move

There are 4 types of friction 4) Fluid friction: occurs when an object moves through a gas or liquid

F = maF = maF = maF = ma F = maF = maF = maF = ma Force and acceleration are related. Newton’s Second Law: Force = Mass X Acceleration 120 kg Lineman Scenario # 1 Look at the situation above. If the acceleration 3 m/s 2 from the snap was equal between these players, then who would have the advantage of force? Lineman = 3 m/s 2 x 120 kg is 360 N Center = 3 m/s 2 x 100 kg is 300 N The Lineman has the advantage. 100 kg Center Scenario # 2 Now, let’s say the Center has a 1 m/s 2 advantage over his opponent at an acceleration of 4 m/s 2 from the snap. Now who has the advantage of force? Lineman = 3 m/s 2 x 120 kg is 360 N Center = 4 m/s 2 x 100 kg is 400 N Now, the Center has the advantage.

Solving Force Problems Step 1 Read the problem. Draw a picture. Step 2Write down what you know. What are you trying to find? Step 4Plug-in the numbers. Solve. Step 3Set up the formula.

“How much force is needed to accelerate a 1400 kg car 2 m/s 2 ? ” Consider the problem… F = m = a = FormulaPlug-inAnswer Units, units, units! Step 1Read the problem. Draw a picture kg car 2 m/s 2

F = m = a = FormulaPlug-inAnswer Units, units, units! 1400 kg 2 m/s 2 Step 2Write down what you know. What are you trying to find? 1400 kg car 2 m/s 2 “How much force is needed to accelerate a 1400 kg car 2 m/s 2 ? ” How much force?

FormulaPlug-inAnswer Step 3Set up the formula. F = m = a = 1400 kg 2 m/s 2 m x a “How much force is needed to accelerate a 1400 kg car 2 m/s 2 ? ” F = m x a

FormulaPlug-inAnswer Units, units, units! Step 4Plug-in the numbers. Solve. 2800kg x m/s 2 or N for newtons…it’s easier to write! F = m = a = 1400 kg 2 m/s 2 “How much force is needed to accelerate a 1400 kg car 2 m/s 2 ? ” F = ma 1400 kg x 2 m/s kg x m/s 2

HELPFUL HINTS: a = F / m F = m x a m = F / a F M A

There are 2 kinds of forces 1) Normal force : the force a surface exerts on an object that is pressing on it

There are 2 kinds of forces 2) Net force : the sum of two or more forces on an object

Newton’s Third Law: Action Forces = Reaction Forces For every action there is an equal and opposite reaction. Look at the picture below: What is the action? What is the reaction? As the gases push downward out of the rocket, The rocket is pushed upward by gases.

An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration For every action there is an equal and opposite reaction.

The Story of Newton’s Apple Newton sat under an apple tree, and an apple fell on his head. That falling apple gave him a revelation GRAVITY. But DON’T think of gravity as falling… It is the pull (force) that an object has on another object. and led him to describe a force called

Gravity is the force that ALL objects in the UNIVERSE exert between each other... 2 things Newton said that gravitational force depends on 2 things: DISTANCE The DISTANCE of the objects MASS The MASS of the objects Less gravitational force compared to... more gravitational force here blue objects green objects blue objects MASS The blue objects have more gravitational force between them than the green objects. This is because the blue objects have more MASS. M o r e F g L e s s F g