Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Physics Newton’s Laws And Forces Aristotle on motion Aristotle believed objects had either “natural” or “violent” motion He also said everything would naturally STOP moving GALILEO: Since he experimented to get EVIDENCE for his conclusions, he is considered to be the father of experimental physics. He also figured out that… Things in motion tend to STAY IN MOTION; they do NOT tend to SLOW DOWN OR STOP ON THEIR OWN. In fact, Galileo figured out that it TAKES a force to make something slow down or stop. The usual force is (he discovered): FRICTION. So in fact, GALILEO figured out the principle behind what we call Newton’s 1st Law NEWTON’S 1ST LAW An object at rest tends to stay at rest, and an object in motion tends to stay in motion in a straight line at constant velocity unless acted on by an outside net force. INERTIA refers to Newton’s 1st Law Inertia is a measure of an object’s RESISTANCE to CHANGE in state of motion. The word inertia comes from the Italian word for “laziness.” Inertia is DIRECTLY PROPORTIONAL TO MASS ONLY. INERTIA IS NOT A FORCE!!! IT IS A TENDENCEY OR CHARACTERISTIC! What is the difference between mass and weight? MASS is the amount of MATTER in an object. Mass does NOT change, regardless of location. Mass is measured in kg. WEIGHT is the pull due to gravity. –Weight CHANGES due to location! –Weight is a FORCE! inertia… If you are floating around in space outside the space shuttle, and go up to it and give it a kick, what will be the results? Newton gives credit to Galileo Since Galileo took all the heat for speaking up about new ideas and empirical evidence, Newton gives him credit, saying: “If I have seen far, it is because I have stood on the shoulders of giants.” What is force? A push or a pull. A NET force is the leftover (or unbalanced) amount of force after you add up all the forces acting in a certain direction. (examples in a sec…) Only NET forces cause accelerations! No net force means NO CHANGE. Newton’s 2nd Law: The acceleration of a body is directly proportional to the net force on it, and inversely proportional to the mass. This means Fnet = ma, but is usually just written F = ma FORCE UNITS Think of Newton’s 2nd law: F=m a N = kg m/s2 Since mass is in kg, and a is in m/s/s, or m/s2, F or Forces are measured in kg m/s2. That is the SAME as a Newton, or N. F = ma 100N = 100kg X 1.00m/s2 a = F/m 1.00m/s2 = 100N / 100kg …Newton’s 2nd Law… This makes sense…the more massive something is, the harder it is to accelerate. And the more force there is, the easier something will accelerate. Zero net force means zero acceleration. F = ma W = mg To calculate weight in metrics: Example: A 15 kg border collie weighs how much? F = ma or W = mg = 15 kg x 10m/s2 = 150 kg m/s2 or 150 N [Newtons] F = ma W = mg A 2 kg mass accelerating at 3 m/s2 has how much net force on it? If you weigh 150 pounds, your mass is about 68 kg. (1 kg = 2.2 lbs.) What is your WEIGHT in Newtons here on Earth? SOLUTIONS A 2 kg mass accelerating at 3 m/s2 has how much net force on it? F = ma = 2kg X 3 m/s2 = 6 N If you weigh 150 pounds, your mass is about 68 kg. (1 kg = 2.2 lbs.) What is your WEIGHT in Newtons here on Earth? W = mg = 68kg X 10m/s2 = 680 N F = ma a = F/m A force of 16 N is pulling on a 2 kg wagon. If there is no friction, how fast is the wagon accelerating? If the wagon above is going at a CONSTANT VELOCITY with the 16N pull, how much friction is there? A force of 16 N is pulling on a 2 kg wagon. If there is no friction, how fast is the wagon accelerating? a = F/m = 16N / 2kg = 8 m/s2 If the wagon above is going at a CONSTANT VELOCITY with the 16N pull, how much friction is there? 16 N ! If going constant velocity, acceleration is 0, & net force is 0 so all forces are BALANCED (equal) in any 1 direction. Newton’s 3rd Law: Every action [FORCE] has an equal and opposite reaction [FORCE]. There are NO single forces. They are always an action/reaction pair.” For example, you touch the table with 1N of Force, it touches you back with 1N of Force SIMULTANEOUSLY (not a little later!). Newton’s 3rd Law says that an action reaction pair would be hands pushing on barbell, barbell pushing on hands. Then HOW can the barbell be ACCELERATED upward? What OTHER action reaction pairs are involved? More on Newton’s 3rd… If you smash the wall with your fist with 80 N of force, the wall will hit you right back with 80 N. But what if you hold a piece of paper in the air and try to hit it with 80 N? If the paper … cannot support or hit you back with 80 N, can YOU really hit IT with 80 N? If the paper can only hit you back with 5 N, what happens to the other 75 N from your punch??! HINT: How do they accelerate? Many forces act at ANGLES Force of friction Opposes motion Occurs between surfaces in contact Ff = μ FN Considered “two dimensional” motion. Remember that horizontal and vertical are COMPLETELY INDEPENDENT of each other!!! LINK TO APPLET FOUR TYPES OF FORCES Right now we think there are 4 different types of forces. Einstein was working on a “unified force theory” before he died, and others continue that work today, believing that there is really only one type of force. The four types of forces (weakest to strongest) are: 1. 2. 3. 4. Gravitational Weak [Nuclear] Electromagnetic Strong [Nuclear] Gravitational force… Is the WEAKEST of all the forces, but acts over the GREATEST distances! You are pulling and pulled by EVERY ATOM IN THE UNIVERSE!!! The FORCE of gravity=G (the gravitational constant 6.67 X 10-11 N m2 / kg2) X mass1 X mass 2 divided by the square of the distance between the two objects (center to center) Electromagnetic forces… Are the forces that act due to electron configuration in atoms These forces are responsible for the PROPERTIES or characteristics of elements, compounds, and materials This force makes paint stick to a wall, makes diamonds extremely hard, makes gold malleable, rubber stretchy, water a bipolar molecule, etc. Strong nuclear force… This is the STRONGEST OF ALL forces, but acts over the SMALLEST distances—only within the nucleus of an atom! What do like charges normally “try” to do? Strong nuclear force binds protons (and neutrons if present) VERY tightly together in the nucleus of an atom. It takes a nuclear fission reaction to break these protons apart. Weak nuclear force… Is the force involved with radioactive decay, where unstable elements give off radiation (alpha, beta, gamma) Great site: overview of forces and Newton’s laws