Force, Gravity and Newton’s Laws Vocabulary Gravity: The fundamental force of attraction that all objects with mass have for each other Force: A push or pull that causes something to change its motion Friction: A force that occurs when two things move past each other and rub together

Isaac Newton & Force Identification

Sir Isaac Newton 1643-1727 Acclaimed as one of the foremost scientific intellects of all time. Credited with works in Mechanics, Astronomy, Philosophy, Mathematics, Optics & Theology

Sir Isaac Newton Principia Philosophiæ Naturalis Principia Mathematica "Mathematical Principles of Natural Philosophy” published in 1687 In this work, Newton described universal gravitation & 3 Laws of Motion

Newton’s Tomb in Westminster Abbey What is a Force? Newton’s Tomb in Westminster Abbey Push or pull that acts on an object Can cause: A resting object to move Acceleration Changes in speed & direction New Unit! Guess what it is? Newton (N)

But first… the scientists who came before… Newton wasn’t the first person to come up with this idea… Aristotle (384-322 B.C.) started the conversation with the proposal that force is required to keep an object moving However, his concept was proven incorrect…

Galileo Galileo (1564-1642) was next… Concluded that moving objects not subjected to friction or other forces would continue to move indefinitely

Descartes Descartes (1596-1650) was certainly on Newton’s list of study. Published "Principles of Philosophy” "that each thing, as far as is in its power, always remains in the same state; and that consequently, when it is once moved, it always continues to move."

Identifying Forces Friction A force that opposes motion of objects “in contact” as they pass each other “In contact” means solid objects touching or objects moving through liquid/gas 4 types: Static, Sliding, Rolling, Fluid (Air resistance)

Identifying Forces Gravity Force that acts between any two masses An attractive force that pulls objects together Does not have to be in contact! Causes objects to accelerate (9.8 m/s2, remember?)

Combining Forces Force is a vector! What does that mean again? Net force – overall force on an object after all the forces are combined Balanced force – net force of zero, which causes no change in motion Unbalanced forces – the net force is not zero causing object to accelerate

Recap What are the 3 things a force can cause? Gravity is a(n) _______________ force that pulls ________ two objects together. How do balanced and unbalanced forces affect the motion of an object?

Newton’s First Law Vocabulary Newton’s Laws: Three laws that explain the motion of objects caused by forces Inertia: The tendency of objects to keep on doing what they are already doing (moving or staying at rest Momentum: The product of an object’s mass and its velocity

Newton’s 1st Law & Momentum Introductory Video for First Law!

Newton’s 1st Law of Motion The state of motion of an object does not change as long as the net force is zero Known as the Law of Inertia What is inertia? The tendency of an object to resist a change in motion!

Newton’s First Law Let’s summarize… An object moving wants to remain in motion with the same speed and direction An object at rest wants to stay at rest Things want to keep doing what they are already doing! IF THE NET FORCE ON AN OBJECT IS ZERO, THE MOITON OF THE OBJECT DOES NOT CHANGE!

Balanced versus Unbalanced Forces Balanced forces cause NO change in an object’s velocity! Unbalanced forces acting on an object cause the object to start moving!

Momentum Mass on the move. Product of mass and velocity. An object with a large momentum is hard to stop ρ = mv ρ -momentum (kg m/s) Bill Nye Video Clip….Momentum! www.youtube.com/watch?v=y2Gb4NIv0Xg

Recap Who were Isaac Newton’s predecessors that influenced his first law? Summarize what inertia means. What would have more momentum, a soccer ball or a bowling ball? Why?

Newton’s Second Law Vocabulary Mass: How much matter there is in an object Weight: The force of gravity acting on an object

Newton’s 2nd Law Introductory Video to Newton’s 2nd Law

Newton’s 2nd Law A net force acting on an object causes the object to accelerate in the direction of the force The acceleration determined by two factors. Size of the force. Mass of the object.

Don’t you already know this? Heavier (more massive) objects require more force to move…Ouch… the same distance.

Some additional summaries: Object accelerates in the direction you apply the force. Acceleration is directly proportional to the force. (What does that mean?) Acceleration is inversely proportional to the mass. (What about this one?)

Newton’s 3rd Law Introductory Video for Newton’s 3rd Law

Newton’s 3rd Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force Known as Action-Reaction forces

Be careful of misconceptions… Action – Reaction forces do not necessarily cancel Why? The forces do not act on the same object! Swimmer’s force is acting on the water. What about the water?

Let’s try some. Press your hands on the edge of your desk. Describe the skin around where the contact is being made. Is it different if you weren’t pushing on the desk? Why does your hand that presses on the desk look more distorted? The desk is pushing on you! Anything you can feel is something pushing on you.

Newton’s 3rd Law & Review Video www.youtube.com/watch?v=cP0Bb3WXJ_k Stops at about 4 minutes.

Recap What does Newton’s 3rd law State? Explain why the forces do not necessarily cancel. Explain how letting the air out of a balloon could describe Newton’s 3rd law.

There is an equation! F = ma F – force m – mass a – acceleration What are the units? Remember Newton? Try some!

Weight vs. Mass Remember the definitions? Mass – amount of matter Weight – force of gravity Notice that weight is a force? W = mg Let’s compare this to F=ma

Recap Describe how F = ma accurately explains Newton’s 2nd Law. Provide an example of Newton’s 2nd Law in your everyday life. How is mass different from weight?