1. Physics Notes - Chapter 2 o 2.2: Speed is a measure of how fast something is moving. It is the rate which distance is covered. ο§ The word rate is a clue that something is being divided by time. Speed is always measured in terms of a unit of distance divided by a unit of time. ο§ Instantaneous Speed: A speed at any instant. ο§ o π΄π£πππππ π ππππ = (πππ‘ππ πππ π‘ππππ πππ£ππππ) (ππππ πΌππ‘πππ£ππ) 2.3 ο§ o Velocity: ο· The difference between speed and velocity is velocity has a direction. ο§ Constant Velocity ο· From the definition of velocity, it follows that to have a constant velocity requires both constant speed and constant direction. Constant speed means that the motion remains at the same speed. ο· Motion at constant velocity is motion in a straight line at constant speed. ο§ Changing velocity ο· If either the speed or the direction is changing, then the velocity is changing. Constant speed and constant velocity are not the same. ο· In a car there are three controls that are used to change the velocity. Gas, break, steering. 2.4 Acceleration: π΄ππππππππ‘πππ = ο§ The rate at which the velocity is changing is called acceleration. Because acceleration is a rate, it is a measure of how the velocity is changing with respect to time. What defines acceleration is change. Acceleration applies to decreases as well as increases in speed. This is often called deceleration, or negative acceleration. Acceleration, like velocity is directional. If we change either speed or direction, or both. We change velocity. And we accelerate. When straight-line motion is considered, it is common to use speed and velocity interchangeably. ο§ ο§ ο§ ο§ ο§ ο§ o (πβππππ ππ π£ππππππ‘π¦) (ππππ πππ‘πππ£ππ ) ο§ π΄ππππππππ‘πππ (πππππ π π π‘ππππβπ‘ ππππ) = πβππππ ππ π ππππ π‘πππ πππ‘πππ£ππ ο§ Speed and velocity are measured in units of distance per time. 2.5 Free Fall, How Fast: ο§ Starts from a rest position and gains speed as it falls ο§ ο§ ο§ ο§ ο§ ο§ ο§ ο§ ο§ ο§ ο§ ο§ - The apple gains more speed during the time it drops from a great height than during the shorter time it takes to drop a meter. Apple does accelerate as it falls. Such an object would be then in a free fall. Freely falling objects are affected only by gravity. The elapsed time is the time that has elapsed, or passed, since the beginning of the fall. Table 2.2 Elapsed Time (Sec) Instantaneous Speed (M/s) 1 10 2 20 3 30 4 40 . . T 10(t) During each second of fall the instantaneous speed of the object increases by an additional 10 meters per second. This gain in speed per second is acceleration. The letter g represents acceleration. (Gravity) π Gravity is 9.81 π 2 π£ = ππ‘ V symbolizes both speed and velocity Instantaneous speed at point of equal elevation in the path is the same whether the object is moving upward or downward. Hang time: The total time than an object stays in the air when something is thrown. What goes up must come down. Chapter Three o 3.4 Projectile Motion ο§ A rolling ball moves as constant velocity. ο§ The ball covers equal distances in equal intervals of time shown ο§ IN the vertical direction, there is a force due to gravity. ο§ The horizontal component of motion for a projectile is completely independent of the vertical component of motion. ο§ Their combined effects produce the variety of curved paths that projectiles follow. ο§ The first is that the ball’s horizontal component of motion remains constant. The ball moves the same horizontal distance in the equal time intervals between each flash, because no horizontal component of force is acting on it. Gravity acts only downward, so the only acceleration of gravity is the ball downward. ο§ The second thing to note is that both balls fall the same vertical distance in the same time. ο§ The path traced by a projectile accelerating only in the vertical direction while moving at constant horizontal velocity is a parabola. o 3.5 Upwardly Launched projectiles. ο§ ο§ - Shoot a projectile skyward at some angle and pretend there is no gravity. After so many seconds t, it should be at a certain point along a straight-line path. But due to gravity, it isn’t. Notice that the horizontal component is always the same and that only the vertical component changes. Note also that the actual resultant velocity vector is represented by the diagonal of the rectangle formed by the vector components. At the top of the path the vertical component shrinks to zero, so the velocity there is the same as the horizontal component of velocity at all other points. Chapter 4 o 4.3 Galileo on Motion: FRICTION ο§ A force is any push or poll. Friction is the name given to the force that acts between materials that touch as they move pas each other. Friction is caused by the irregularities in surfaces of objects that are touching. ο§ If friction were absent a moving object would need no force whatever to remain in motion ο§ Argued that only when friction is present is a force needed to keep an object moving. ο§ Inertia is when a material object is resisting to a change in motion. o 4.4 Newton’s law of inertia ο§ Every object continues in a state of rest, or of motion in a straight line at a constant speed, unless it is compelled to change that state by forces exerted upon it. o 4.5 Mass – A measure of inertia. ο§ The amount of inertia an object has depends on its mass. Which is roughly the amount of material present in the object, the more mass an object has, the greater its inertia and the more force it takes to change its state of motion. ο§ Mass is a measure of the inertia of an object. ο§ Volume is a measure of space and is measured in units such as cubic, centimeters, cubic meters, and liters. ο§ Mass is measures in kilograms. ο§ Mass is more fundamental than weight. Mass is a measure of the amount og material in an object and depends only on the number of and kind of atoms that compose it. ο§ Weight is a measure of the gravitational force acting on the object ο· Weight depends on an objects location ο§ The amount of material in a particular stone is the same whether the stone is located on the earth, on the moon, or in outer space. Hence, the stone’s mass is the same on all of these locations ο§ Mass is the quantity of matter in an object. More specifically, mass is a measure of inertia, or laziness. That an object exhibits in the response to any effort made to start it, stop it, or otherwise changes its state of motion ο§ Weight is the force of gravity on an object. ο§ - They are proportional to each other in a given place. Objects with great mass have great weights: objects with little mass have little weight. In the same location, twice the mass weighs twice as much. ο§ One kilogram is 9.81 Newtons. ο§ π€πππβπ‘ = ππ o 4.7 Equilibrium – When Net Force Equals Zero: ο§ Support force is the force acting the other way on an object. Table Chair such ο· Often called normal force ο§ When an object is at rest, with the net force on it being zero, we say the object is in a state of equilibrium. The resting book is in equilibrium. Chapter 5 o 5.1 Force Causes Acceleration ο§ Acceleration depends on the net force ο§ The force we apply is not the only force acting on an object. Other forces may act on it as well. ο§ π΄ππππππππ‘πππ = ππππππ‘πππππππ¦ πππππππ‘πππππ π‘π = πππ‘ πππππ. o 5.2 Mass resists Acceleration ο§ For a given force, the acceleration produces is inversely proportional to the mass ο§ o 5.3 Newtons Second Law ο§ The acceleration produces by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object. ο§ o - 1 Acceleration ~ πππ π πΉ π=π 5.5 Applying Force – Pressure πππππ ππππ ππ ππππππππ‘πππ ο§ ππππ π π’ππ = ο§ You exert more pressure against the ground when you stand on one foot than when you stand on both feet. This is due to the decreased area of contact. Stand on one toe like a ballerina and the pressure is huge. The smaller the area supporting a giving force, the greater the pressure on that surface is. Chapter 6 o 6.2 Newtons Third Law ο§ Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. ο§ One force is called the Action Force ο§ The other force is called the reaction force ο§ It doesn’t matter which force we call action and which force we call reaction. The important thing is that they are coparts of a single interaction and that neither force exists without the other. They are equal in strength and opposite in direction. o 6.3 Identifying Action and Reaction ο§ o Sometimes the identity of the pair of action and reaction forces in an interaction is not immediately obvious. ο§ Just identify interacting objects A and B and if the action is A on B, the reaction is simply B on A, in the case of the falling boulder, the interaction during the fall is the gravitational attraction between the boulder and the earth. ο§ If we call the Action the earth exerting a force on the boulder, then the reaction is the boulder simultaneously exerting force on the earth. 6.4 Action and Reaction on Different Masses. ο§ Recall that Newton’s second law states that acceleration is not only proportional to the net force, but it is also inversely proportional to the mass. ο§ ο§ - π π =π Consider a machine fun recoiling each time a bullet is fired. If the machine hun is fastened on a vertical wire so that it is free to slide it accelerates upward as bullets are fired downward. Chapter 8 o 8.4 Potential Energy ο§ The energy that is stores and held in readiness is called potential energy (PE) ο§ The upward force required while moving at constant velocity is equal to the weight mg, of the object, so the work done in lifting it through a height h is the product of mgh. ο· ππππ£ππ‘ππ‘πππππ πππ‘πππ‘πππ ππππππ¦ = ππππβπ‘ ∗ βπππβπ‘ ο· ππΈ = ππβ o 8.5 Kinetic Energy ο§ Push on an object and you can set it in motion. If an object is moving, it is capable of doing work. πΎππππ‘ππ πΈπππππ¦ = πππ π ∗ π ππππ2 ο§ πΎπΈ = 2 ππ£ 2 ο§ o 1 2 ο§ 1 Kinetic energy of a moving obkect is equal to the work required to bring it to that speed from rest, or the work the object can do while being brought to rest. ο· πππ‘ πππππ ∗ πππ π‘ππππ = πππππ‘ππ ππππππ¦ 1 ο· πΉπ = 2 ππ£ 2 8.6 Conservation of energy. ο§ The study of the various forms of energy and the transformations from one form into another led to one of the greatest generalizations into physics – the law of conservation of energy. ο§ Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.
