Free Fall A state of motion where an object has a constant acceleration because it is only affected by force of gravity - so there can be no air resistance So to conduct an experiment about free fall, involving an object in a room filled with air… we need to minimize the affects of air by using an object with a lot of mass a little surface area and not letting it fall very far.

Free Fall The object is only affected by one thing – gravity. But where does gravity come from? from the mass of an object the more massive, the more gravity So Earth vs moon vs Jupiter… The value of acceleration caused by gravity here on Earth: g is about 10 m/s2 or more exactly, for math problems… g = 9.8 m/s2

The Value of g It is a measured quantity, so it varies from place to place. Depends on Latitude Altitude

That means, an object in free fall will gain 10 m/s every second as it falls lose 10 m/s every second as it rises maintains 10 m/s2 at the tip top, where v = 0 This is what gets it to change from a temporary v = 0, to moving again on its way back down Otherwise, it would just stay there… weird… These different “forms” of a can be described as just one constant (consistent) a for free fall: g = 10 m/s2, down since gravity always pulls DOWN on things so DOWN accounts for both losing speed as it goes up gaining speed as it goes down

So what if air is an issue??? Then the a ≠ 9.8 m/s2 , down nor is it even a set, constant value - we’ll learn more about this in Ch 5… Characteristics of an object that affect how it falls when there’s air present: mass shape / surface area (Note we never deal with these in “free fall” situations, as they don’t matter -- everything falls identically in free fall!) But sometimes these characteristic provide unexpected results, watch… So thank goodness we’re dealing with free fall!

The (5) Constant Acceleration Equations able to be used any time an object undergoes constant acceleration so they work for, but aren’t limited to, objects in free fall! deal with the 5 physical quantities we’ve been working with so far Δt Δd vi vf and a But each eq’n only contains 4 of these 5 variables Watch….

Constant Acceleration Equations missing variable? Δd vf vi Δt a vf = vi + aΔt Δd = vi Δt + ½ a Δt2 Δd = vf Δt - ½ a Δt2 vf2 = vi2 + 2a Δd Δd = (vi + vf) Δt 2 To use these equations, you will be given a problem that contains 3 given pieces of information and 1 unknown so that 1 of the 5 variables is completely left out: choose the equation that is missing that ignored variable. Try some…

Ex 1. A car, starting at 28 m/s, accelerates at a constant rate so that in 5.3 s, it was going 52 m/s. How far did the car travel in this time? 212 m

Ex 2. A motorcycle ends up traveling at 47 m/s after having undergone a constant 1.7 m/s2 acceleration over 184 m. What was its starting speed? 39.8 m/s

Ex 3. A ball is thrown straight up, reaching a maximum height of 71 m Ex 3. A ball is thrown straight up, reaching a maximum height of 71 m. How long does this take? 3.8 s