Chapter 8: Newton’s Laws notes Section 8-1 I. The study of: a. Chemistry is the study of atoms/structure/matter and how it interacts. b. Physics is the study of those atoms/matter in motion. II. Motion is the change of position. a. Motion can be described 2 ways: i. Distance (traveled) ii. Displacement (distance between starting and ending points) b. Motion is relative to position. Things closer may seem to move faster. III. Measuring Motion a. Speed=distance divided by time (s=d/t) measured in m/s b. Velocity is speed with a direction c. Acceleration is the change in speed over time i. Formula: Acceleration= (final speed – initial speed)/time ii. Measured in m/s2 (read as meters per second squared) Section 8-2 IV. Question: Name 2 forces that don’t require direct contact. a. Magnetism (magnets) b. Gravity (all things with matter have gravity) V. Force-a push or a pull a. SI unit for force is the Newton (abbreviated as ‘N’) b. Formula: Force = mass times acceleration (F=ma) c. The different variables are measured in: i. Mass measured in kilograms (kg) ii. Acceleration measured in meters per second squared (m/s2) iii. Force measured in Newtons (N) VI. Newton’s First Law of Motion (parts A & B) a. An object at rest will remain at rest unless acted on by an unbalanced force. b. An object in motion in a straight line will remain in motion in a straight line unless acted on by an unbalanced force. VII. Inertia a. Newton’s 1st law of motion is sometimes called the law of inertia. b. Definition of inertia—resistance to change. i. If something is at rest, it resists changing it to motion. ii. If something is in motion, it resists changing it to stop or speed up. c. If mass increases, inertia increases. If mass decreases, inertia decreases. VIII. Understanding Forces a. ‘At rest’—balanced forces. No movement. b. ‘In motion’—unbalanced forces. Movement or change of direction. Section 8-3 IX. Law uses a. 1st law helps predict when an object’s motion will change. b. 2nd law helps explain the motion of that object. X. Newton’s Second Law of Motion a. An object acted on by an unbalanced force will accelerate in the direction of that force. b. Formula of 2nd law: acceleration (m/s2) = force (N) divided by mass (kg) c. Shorthand formula: a = F/m d. Formula rewritten: F=m*a (Force = mass times acceleration) e. Formula rewritten: m = F/a (mass = Force divided by acceleration) XI. Gravitational force is the amount of force between 2 objects. a. The more mass an object has, the more gravity it has. (Think sun and earth) b. The acceleration of earth’s gravity exerted on all things on earth is at the rate of 9.8 m/s2. Earth’s acceleration: 9.8 m/s2. c. Weight is the force of earth’s gravity on the mass of an object. i. To find the weight of an object, use the formula F = m*a. ii. Example: mass of boulder is 1000 kg. 1. m= 1000 kg, a = 9.8 m/s2 (earth’s acceleration) 2. F = 1000 kg * 9.8 m/s2 3. F = 9800 N XII. Friction is the force between to objects that resists motion (rubbing). a. Static friction is the friction that helps keep things in place. b. Sliding friction is the force that slows things down as it slides across a surface. c. Rolling friction is the force that allows objects to roll (this reduces friction). d. Air resistance is the force of air molecules resisting movement. Section 8-4 XIII. Newton’s 3rd law of motion a. For every action, there is an equal and opposite reaction. b. In other words, all forces act in PAIRS. XIV. Action & Reaction a. Action force—amount of force applied at the beginning b. Reaction force—equal to action force; the 2nd force. XV. Applying the 3rd law a. The greater the action, the greater the reaction. b. Unlike balanced forces, action and reaction forces can cause the motion of objects to change. XVI. Using Friction a. To make you go or stop, forces that are applied usually need friction.
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