Linear Motion Are you moving? How do you know? Earth spins on axis at 700 mph Earth revolves around sun 72,000 mph Solar system moves thru galaxy 675,000 mph So I ask again, Are you moving?? Best answer is another question: Relative to what? To what frame of reference are we judging motion? Since all motion is really measured relative to a particular background. The typical frame of reference we assume, if none is stated, is that of the Earth, so with that, are you moving? No, in your chair, you’re above the same spot on Earth.

Speed Measures how fast something moves or the rate at which distance is covered Rate is any quantity that involves dividing by time Ex… The equation to find speed: v = d/t where v is for speed (and eventually velocity) d is the distance or displacement t is the time interval past units: any distance unit / any time unit Ex:

Explaining Table 2.1 on pg 12: It is just for estimation purposes – it does not give an exact conversion, but that’s OK, that’s all I’ll want! Really what you’ll need to do most often is turn a “new” unit into the one you know (mph), so x m/s x 2 ≈ ____ mph and x km/h ÷ 2 ≈ ____ mph Try some: 10 m/s ≈ 110 km/hr ≈ 346 m/s ≈ 43.7 km/h ≈

2 Types of Speed Instantaneous – at a given instant - to know it, look at a speedometer Average – over the course of a that lasts longer than an instant –doesn’t provide info on mins or maxs –eq’n: v avg = total distance / total time Why not add up individual speeds and divide by how many there are? If you spend different amounts of time at each speed, it won’t work out.

Velocity Provides information about both speed & direction Ex: 60 mph vs 60 mph, North (Doesn’t seem like a big difference, but it can be and we’ll be seeing examples of that later…) 2 Types of Velocity Constant – the object maintains the same speed in the same direction (straight line) Changing – the object changes either speed OR direction So which for a horse on a Merry-Go Round? changing due to circular path - direction What 3 means does a car have to change v? brake, gas and steering wheel

Acceleration Is the rate at which velocity CHANGES – so you are either speeding up, slowing down OR turning If not doing one of these, then a = 0! It does not measure how fast you’re going, it measures how fast you’re changing how fast you’re going! It does not mean “to be moving fast” –You could have a high v, but a low or 0 a: Ex: –You could have a low or 0 v, but a high a: Ex:

Equation for math problems: a = v f – v i t where v f is final velocity and v i is initial velocity –This eq’n reinforces that there must be 2 different velocities for an object to accelerate –Often one of them will = 0, but must state that as part of the given and insert it into the original eq’n Units: Any speed units / any time units Examples mph / s as in “this Audi R8 does 0 to 60 in 4.6 seconds” km/h / s if you lived in any other country…

–What might need units of m/s / hr for its acceleration? Something that accelerates very slowly – like –Standard acceleration unit in physics: m/s / s (or m/s 2 ) But you must say & write this as “Gains/loses (#) m/s every second” Let’s do some examples: A toy truck goes 3 m/s the 1 st time we look 5 m/s 1 second later 5 m/s 1 second later 7 m/s 1 second later 7 m/s 1 second later What’s its acceleration? a = gaining 2 m/s every sec A plane landing goes 50 m/s the 1 st time we look 40 m/s 1 second later 30 m/s 1 second later What’s its acceleration? a = losing 10 m/s every sec

Let’s try a few examples… Ex #1. A car took off from a red light and reached 27m/s in 5.8 s. What was its acceleration? 1 st, list the given & unknown as variables: 2 nd, provide the original equation: 3 rd, plug the numbers into the equation: 4 th, solve for an answer – does it make sense? - box it in: gains 4.65 m/s every s

Ex #2. A jet plane, moving at 253 m/s, runs into a storm which causes it to slow to 175 m/s in 38 s. What was its acceleration? loses 2.05 m/s every s

Ex #3. A robot’s specifications says it can accelerate at 1.5 m/s 2. If its “forward” button is held on for 17 s, how fast should it be going? 25.5 m/s