time distance speed =
time distance speed =
time distance speed =
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Speed• Speed is a measure of how fast something ismoving.• It is the rate at which a <strong>distance</strong> is covered• Units of <strong>speed</strong> could be: km/h, m/s, mi/h, ft/s• In physics we use units of m/s for <strong>speed</strong>d• s = d/t<strong>speed</strong> =<strong>distance</strong><strong>time</strong>st
Instantaneous Speed• Instantaneous <strong>speed</strong> is <strong>speed</strong> at any instant in<strong>time</strong>.• A <strong>speed</strong>ometer measures <strong>speed</strong> in ‘real <strong>time</strong>’(the instantaneous <strong>speed</strong>).
Average Speed• Average <strong>speed</strong> is the average of allinstantaneous <strong>speed</strong>s; found simply by a total<strong>distance</strong>/total <strong>time</strong> ratio• The average <strong>speed</strong> of a trip:total <strong>distance</strong>average <strong>speed</strong> =elapsed <strong>time</strong>• For more informationhttp://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L1d.html
Velocity and Speed• In physics we distinguish between <strong>speed</strong> and velocity:• Speed refers to how quickly an object moves (a scalarquantity).• Velocity is defined as <strong>speed</strong> in a given direction or rate ofchange of position (displacement over <strong>time</strong>). v = x/t• Velocity refers to both the <strong>speed</strong> and direction of motion ofan object (a vector quantity).• Negative velocity means the object is moving in the oppositedirection• Motion at constant velocity means that both the <strong>speed</strong> anddirection of an object do not change.• In a car, we can change the velocity three ways: gas pedal to<strong>speed</strong> up, brake to slow down or steering wheel to changedirection
Velocity Triangle• Speed and velocity triangles are similarbecause v = x/t• Find the equation for displacement, and <strong>time</strong>using the triangle• x = v x t• t = x/vxvt
Speed vs. VelocityAverage Speed(scalar)Distance TraveledTotal <strong>time</strong>Average Velocity(vector)DisplacementTotal <strong>time</strong>Velocityhas adirection!!r∆x∆xv=v=∆t∆t
Try itCalculate the average <strong>speed</strong> and averagevelocity of a complete round-trip in which theoutgoing 200 km is covered at 90 km/h,followed by a one-hour lunch break, and thereturn 200 km is covered at 50 km/h.Average <strong>speed</strong> = 60 km/hAverage velocity = 0
Velocity Questions1) How far does Bob run if he maintains an averagevelocity of 3 m/s for 10 s?2) List three ways you can change the velocity of yourcar.3) Is it possible to go around a corner withoutchanging velocity? Explain.4) One car is going 25 miles/hr north, another car isgoing 25 miles/hr south. Do they have the samevelocity? Explain.
Change language