chapter 2 accelerated motion vocab Sy s t e m a t i c e r ro r, r a n d o m e r ro r, h a l t , stationar y, initial, final, steadily, apply, uniform, gradient, multiflash, free fall, circuit, magnet, value, scatter, uncertainty, friction, air resistance, twice, stop watch, parabola, angle, t h ro w, p ro j e c t i l e , ve r t i c a l , h o r i z o n t a l , separately, resolve, cosine, sine, tangent, graph velocity is constant, zero, positive, negative, or changing ? acceleration is constant, zero, positive, negative, or changing ? V 0 t graph velocity is constant, zero, increasing, decreasing or negative? decreasing acceleration is constant, zero, positive, negative, or changing ? constant and negative V 0 t chart velocity acceleration constant zero positive negative v changing V 0 t v graph constant Could you draw: zero positive negative V changing t velocity acceleration v v v v v v v v v measuring acceleration measuring acceleration How many measure points we need to find: velocity, acceleration measuring velocity 2 measuring points V = displacement / time = (s2-s1)/(t2-t1) S (t2, s2) (t1, s1) t measuring acceleration at least 3 measuring points a = change in velocity / time = (v2-v1)/(t2-t1) v1 = (s2-s1)/(t2-t1) v2 = (s3-s2)/(t3-t2) S (t3, s3) (t2, s2) (t1, s1) t measurements using light gates 4 measure points: t1, t2, t3, t4 t1 t2 l1 t4 t3 l2 light gate average speed at t1 is u average speed at t3 is v t1 t2 l1 t4 t3 l2 light gate u = l1/(t2-t1) v = l2/(t4-t3) a = (v-u)/(t3-t1) t1 t2 l1 t4 t3 l2 measuring using ticker-timer from slow to fast measuring using ticker-timer cut each section start slow fast measuring using ticker-timer place them side by side draw a line from slow to fast find slope of a line slope is acceleration fast slow start equations of motions introduction should you run or stop at yellow light? 5 variables s = displacement a = acceleration u = initial velocity v = final velocity t = time taken equations of motions how to use equations of motions find what we know number for variables u, a, t, v, s find what we want to know which variable? find the right equations of motions substitude and calculate problem A street is 10 m wide. Yellow light last for about 5 s. You know your top speed is 6m/s. You stand at one end of the street when traffic light turn yellow. Should you run or stop? problem A street is 10 m wide. Yellow light last for about 5 s. You stand at one end of the street when traffic light turn yellow. How much you need to accelerate to cross? a=? s = 10m t = 5s u=0 v - don't care problem A street is 10 m wide. Yellow light last for about 5 s. You stand at one end of the street when traffic light turn yellow. How much you need to accelerate to cross? a=? s = 10m t = 5s u=0 v - don't care use equation problem a = ?, s = 10m t = 5s, u = 0 v - don't care 10 = a*25/2 a = 2m/s^2 As long as you can accelerate at 2m/s^2 you could cross the street. problem a train accelerates steadily from 4.0m/s to 20m/s in 100s. a. calculate the acceleration of the train. b. from its initail and final velocitites, calculate the average velocity of the train. problem a train accelerates steadily from 4.0m/s to 20m/s in 100s. a. calculate the acceleration of the train. problem a train accelerates steadily from 4.0m/s to 20m/s in 100s. a. calculate the acceleration of the train. given: u = 4.0, v = 4.0, t = 100, ask: a = ? use equation: v=u+at rearrange equation problem a train accelerates steadily from 4.0m/s to 20m/s in 100s. b. from its initail and final velocitites, calculate the average velocity of the train. use equation: v average = (v-u)/2 problem a train accelerates steadily from 4.0m/s to 20m/s in 100s. c. calculate the distance travelled by the train in this time of 100s. problem a train accelerates steadily from 4.0m/s to 20m/s in 100s. c. calculate the distance travelled by the train in this time of 100s. know: u = 4.0, v = 4.0, t = 100, want: s = ? use answer for part a use equation: s = ut +at^2/2