* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download what is physics
Derivations of the Lorentz transformations wikipedia , lookup
Inertial frame of reference wikipedia , lookup
Relativistic mechanics wikipedia , lookup
Coriolis force wikipedia , lookup
Specific impulse wikipedia , lookup
Jerk (physics) wikipedia , lookup
Faster-than-light wikipedia , lookup
Fictitious force wikipedia , lookup
Centrifugal force wikipedia , lookup
Velocity-addition formula wikipedia , lookup
Hunting oscillation wikipedia , lookup
Seismometer wikipedia , lookup
Mass versus weight wikipedia , lookup
Newton's theorem of revolving orbits wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Classical mechanics wikipedia , lookup
Equations of motion wikipedia , lookup
Classical central-force problem wikipedia , lookup
MR. SURRETTE VAN NUYS HIGH SCHOOL CHAPTER 7: MOTION CLASS NOTES MECHANICS Simply put, the study of motion is the study of anything that moves. In physics, the study of motion is called mechanics. BRANCHES OF MECHANICS Mechanics is divided into two branches: kinematics and dynamics. Essentially, kinematics is the “how of motion” (descriptive) and dynamics is the “why of motion” (explanatory). KINEMATICS Kinematics includes the measurement of distance, speed (velocity), and acceleration. SPEED Any object in motion moves a certain distance in a given time. Speed is a measure of how fast something is moving: s=d/t (Speed [m/s] = Distance [m] / Time [s]) TYPES OF SPEED The speed an object has at any given moment is called instantaneous speed. It is the speed shown by the speedometer of a car. It is rare that a car or any other moving body travels an entire distance at the same speed. This is why we usually measure the average speed of the entire trip. Example 1. What is the average speed if a car travels 320 kilometers in 4 hours? 1A. (1) Speed = Distance / Time (2) s = d / t (3) s = 320 km / 4 hours (4) s = 80 km / hour VELOCITY Velocity is speed combined with the direction of motion. When a car travels 60 kilometers per hour, that is the speed of the car. If a car travels 60 kilometers per hour north on the highway, that is its velocity. VELOCITY EQUATION v = d / t (Velocity [m/s] = Distance [m] / Time [s]) CHEMISTRY PAGE 1 MR. SURRETTE VAN NUYS HIGH SCHOOL ACCELERATION When the velocity of an object changes, the object accelerates. Acceleration is the rate of change in velocity: a = v / t (Acceleration [m/s2] = Velocity [m/s] / Time [s]) Example 2. A car goes from rest to 20 m/s in 6 s. What is its acceleration? 2A. (1) a = v / t (2) a = 20 m/s / 6 s (3) a = 3.33 m/s2 FREE-FALL VELOCITY Objects fall to the ground because of Earth’s gravity. When an object falls without friction, it is in freefall. The influence of Earth’s gravity on freely falling objects is represented by the letter g. The value of g is 9.8 meters per second, every second. This means: g = 9.8 m/s2 FREE-FALL VELOCITY For an object falling from rest, the velocity v at time t can be expressed: v = gt Example 3. How fast does a rock in free-fall move after 6 seconds? 3A. (1) v = gt (2) v = (9.8 m/s2)(6 s) (3) v = 58.8 m/s FREE-FALL DISTANCE The distance traveled by an object in free-fall starting from rest is: d = ½ gt2 Example 4. How far does a rock in free-fall travel after 6 seconds? 4A. (1) d = ½ gt2 (2) d = ½ (9.8 m/s2)(6 s)2 (3) d = 176.4 m CHEMISTRY PAGE 2 MR. SURRETTE VAN NUYS HIGH SCHOOL DYNAMICS Kinematics uses distance, velocity, and acceleration to describe motion. Dynamics analyzes motion in terms of forces. The laws of motion were formulated by Isaac Newton three centuries ago. NEWTON’S FIRST LAW Newton’s first law is the Law of Inertia: “an object at rest will remain at rest and an object in motion will remain in motion with a constant velocity unless acted on by a net external force” (force is later defined in Newton’s Second Law). MASS VERSUS WEIGHT Mass is the same as inertia. The greater an object’s mass, the harder it is to change its motion. For example, interstate trucks take much longer to speed up and slow down than motorcycles. MASS VERSUS WEIGHT Weight is a mathematical relationship: w = mg Example 1. Calculate the weight of a 10 kg object on earth: 1A. (1) w = mg (2) w = (10 kg)(9.8 m/s2) (3) w = 98 N (A “newton” is explained in Newton’s Second Law). NEWTON’S SECOND LAW Newton’s second law, the Law of Acceleration, states: “the acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass.” NEWTON’S SECOND LAW Newton’s second law is written mathematically as: F = ma Force [N] = (Mass [kg])(Acceleration[m/s2]. (One Newton is about 0.25 pounds.) Example 2. How much force is needed to accelerate a 3 kg mass by 4 m/s2? 2A. (1) F = ma (2) F = (3 kg)(4 m/s2) (3) F = 12 N CHEMISTRY PAGE 3 MR. SURRETTE VAN NUYS HIGH SCHOOL Example 3. What acceleration is produced by a 10 N force pushing on a 3 kg mass? 3A. (1) F = ma (2) a = F / m (3) a = 10 N / 3 kg (4) a = 3.33 m/s2 FRICTION Friction is a resistive force that opposes the motion of an object. For example, air resistance slows down the motion of falling objects. NEWTON’S THIRD LAW Newton’s third law, the Law of Action-Reaction, states: “when two bodies interact, the force which “A” exerts on body “B” (the action force) is equal in magnitude and opposite in direction to the force which body “B” exerts on body “A” (the reaction force).” NEWTON’S THIRD LAW A consequence of the third law is that forces occur in pairs. Remember that the action force and the reaction force act on different objects. NEWTON’S THIRD LAW Graphically, this can be represented as: Note: Action and Reaction forces occur at the same time. CHEMISTRY PAGE 4