Physics I Honors Mechanics II Acceleration Acceleration

Physics I Honors Acceleration is a vector quantity defined as the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity.vector quantityvelocity

Physics I Honors Acceleration The increase or decrease of velocity per unit time is called acceleration. It is the rate of change of velocity. Acceleration may be –A change in magnitude Or –A change in direction Or –Both Its units are meters per second squared (m/s 2 ).

Physics I Honors …and some notes… Acceleration is a vector. It can be positive or negative. At rest means initial time is zero. When velocity is constant, acceleration is zero. When velocity increases at a constant rate, acceleration is uniform.

Physics I Honors Uniformly Accelerated Motion Along a Straight Line In this case… acceleration is a constant and the acceleration vector lies in the line of the displacement vector.

Physics I Honors Accelerating Objects

Physics I Honors Acceleration Average acceleration is the change in velocity divided by the change in time. Acceleration = change in velocity change in time

Physics I Honors The 5 Acceleration Equations!

Physics I Honors S-t, v-t, a-t graphs for constant acceleration

Physics I Honors Definitions Instantaneous Velocity –the slope of the displacement versus time graph Instantaneous Acceleration –the slope of the velocity versus time graph

Physics I Honors Slopes Displacement Time A B

Physics I Honors Six Cases of Acceleration 1 - speed up in positive direction = positive accel. a + direction v f = 8 m/s v i = 5 m/s t = 3 seconds final initial Calculate average acceleration!

Physics I Honors Six Cases of Acceleration 2 - slow down in positive direction = negative accel. a + direction v i = 8 m/s v f = 5 m/s t = 3 seconds final initial Calculate average acceleration!

Physics I Honors Six Cases of Acceleration 3 - speed up in negative direction = negative accel. + direction v f = -8 m/s v i = -5 m/s a t = 3 seconds final initial Calculate average acceleration! What is happening to speed?, velocity?

Physics I Honors Six Cases of Acceleration 4 - slow down in negative direction = positive accel. final initial + direction v f = -5 m/s v i = -8 m/s t = 3 seconds Calculate average acceleration! What is happening to speed?, velocity?

Physics I Honors Six Cases of Acceleration 5 - reverse directions from pos to neg = negative accel. v f = -1 m/s v i = +1 m/s a + direction t = 3 seconds initial final Calculate average acceleration!

Physics I Honors Six Cases of Acceleration 6 - reverse directions from neg to pos = positive accel. v f = -1 m/s v i = +1 m/s a + direction t = 3 seconds initial final Calculate average acceleration!

Physics I Honors Horizontal Acceleration Consider an airplane taking off. As it goes down the runway it increases its speed until it is going fast enough to “lift off” the ground.

Physics I Honors …but wait a minute… What if it’s vertical straight line motion…say, like a rocket going up at Cape Canaveral?!? When you are traveling in a vertical direction, acceleration is always the same. It is the acceleration of gravity, g, which always has the same value. For vertical motion problems, simply substitute g for a in any of the straight-line motion equations.

Physics I Honors Airborne motion is UNIFORMLY ACCELERATED MOTION the change in velocity over time is linear so we say the change in velocity is constant This constant acceleration is = -9.8 m/s 2 This is the rate at which any airborne object will accelerate.

Physics I Honors Free Fall The force of gravity points downward –Acceleration of gravity near the surface of Earth is called g = 9.8 m/s 2 = 32.1 ft/s 2 Air resistance ignored We have then the conditions of one-dimensional kinematics – straight line motion with constant acceleration.

Physics I Honors 6-9 Gs: "Increased chest pain and pressure; breathing difficult, with shallow respiration from position of nearly full inspiration; further reduction in peripheral vision, increased blurring, occasional tunneling, great concentration to maintain focus; occasional lacrimation; body, legs, and arms cannot be lifted at 8 G; head cannot be lifted at 9 G." 9-12 Gs: "Breathing difficulty severe; increased chest pain; marked fatigue; loss of peripheral vision, diminution of central acuity, lacrimation." 15 Gs: "Extreme difficulty in breathing and speaking; severe vise-like chest pain; loss of tactile sensation; recurrent complete loss of vision. Human Response to Sustained g’s Data primarily from: Bioastronautics Data Book, second edition, 1973, NASA) In certain activities people experience + & - accelerations. By standardizing these accelerations to the normal acceleration on earth (-9.8 m/s/s) you get an idea of how much force they are experiencing

Physics I Honors Problem Solution 1. Draw a picture. 2. List values for any parameters that are given. 3. Find equations in which all of the variables are known except the one that you are trying to find. 4. Isolate 5. Substitute values for variable and solve.