[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:14.00,0:00:17.00,Default,,0000,0000,0000,,Have you ever noticed that it's harder \Nto start pedaling your bicycle
Dialogue: 0,0:00:17.00,0:00:20.00,Default,,0000,0000,0000,,than it is to ride at a constant speed?
Dialogue: 0,0:00:20.00,0:00:23.00,Default,,0000,0000,0000,,Or wondered what causes your bicycle to move?
Dialogue: 0,0:00:23.00,0:00:27.25,Default,,0000,0000,0000,,Or thought about why it goes forward \Ninstead of backwards or sideways?
Dialogue: 0,0:00:27.25,0:00:30.26,Default,,0000,0000,0000,,Perhaps not, and you wouldn't be alone.
Dialogue: 0,0:00:30.26,0:00:31.82,Default,,0000,0000,0000,,It wasn't until the 17th century
Dialogue: 0,0:00:31.82,0:00:34.69,Default,,0000,0000,0000,,that Isaac Newton described \Nthe fundamental laws of motion
Dialogue: 0,0:00:34.69,0:00:37.00,Default,,0000,0000,0000,,and we understood the answer \Nto these three questions.
Dialogue: 0,0:00:37.00,0:00:40.80,Default,,0000,0000,0000,,What Newton recognized was that \Nthings tend to keep on doing
Dialogue: 0,0:00:40.80,0:00:43.69,Default,,0000,0000,0000,,what they are already doing. \NSo when your bicycle is stopped,
Dialogue: 0,0:00:43.69,0:00:46.69,Default,,0000,0000,0000,,it stays stopped, and when it is going,
Dialogue: 0,0:00:46.69,0:00:48.00,Default,,0000,0000,0000,,it stays going.
Dialogue: 0,0:00:48.00,0:00:50.00,Default,,0000,0000,0000,,Objects in motion tend to stay in motion
Dialogue: 0,0:00:50.00,0:00:53.82,Default,,0000,0000,0000,,and objects at rest tend to stay at rest.
Dialogue: 0,0:00:53.82,0:00:55.89,Default,,0000,0000,0000,,That's Newton's First Law.
Dialogue: 0,0:00:55.89,0:00:59.52,Default,,0000,0000,0000,,Physicists call it the Law of Inertia, \Nwhich is a fancy way of saying
Dialogue: 0,0:00:59.52,0:01:03.98,Default,,0000,0000,0000,,that moving objects don't spontaneously \Nspeed up, slow down, or change direction.
Dialogue: 0,0:01:03.98,0:01:09.00,Default,,0000,0000,0000,,It is this inertia that you must overcome \Nto get your bicycle moving.
Dialogue: 0,0:01:09.00,0:01:12.00,Default,,0000,0000,0000,,Now you know that you have to overcome \Ninertia to get your bicycle moving,
Dialogue: 0,0:01:12.00,0:01:14.00,Default,,0000,0000,0000,,but what is it that allows you to overcome it?
Dialogue: 0,0:01:14.00,0:01:18.08,Default,,0000,0000,0000,,Well, the answer is explained by Newton's Second Law.
Dialogue: 0,0:01:18.08,0:01:20.54,Default,,0000,0000,0000,,In mathematical terms, Newton's Second Law says
Dialogue: 0,0:01:20.54,0:01:24.00,Default,,0000,0000,0000,,that force is the product of mass times acceleration.
Dialogue: 0,0:01:24.00,0:01:27.00,Default,,0000,0000,0000,,To cause an object to accelerate, or speed up,
Dialogue: 0,0:01:27.00,0:01:29.00,Default,,0000,0000,0000,,a force must be applied.
Dialogue: 0,0:01:29.00,0:01:31.00,Default,,0000,0000,0000,,The more force you apply,
Dialogue: 0,0:01:31.00,0:01:34.00,Default,,0000,0000,0000,,the quicker you accelerate. \NAnd the more mass your bicycle has,
Dialogue: 0,0:01:34.00,0:01:36.00,Default,,0000,0000,0000,,and the more mass you have too,
Dialogue: 0,0:01:36.00,0:01:39.83,Default,,0000,0000,0000,,the more force you have to use \Nto accelerate at the same rate.
Dialogue: 0,0:01:39.83,0:01:43.65,Default,,0000,0000,0000,,This is why it would be really difficult \Nto pedal a 10,000 pound bicycle.
Dialogue: 0,0:01:43.65,0:01:49.06,Default,,0000,0000,0000,,And it is this force, which is applied \Nby your legs pushing down on the pedals,
Dialogue: 0,0:01:49.06,0:01:52.09,Default,,0000,0000,0000,,that allows you to overcome Newton's Law of Inertia.
Dialogue: 0,0:01:52.09,0:01:54.97,Default,,0000,0000,0000,,The harder you push down on the pedals, \Nthe bigger the force
Dialogue: 0,0:01:54.97,0:01:56.57,Default,,0000,0000,0000,,and the quicker you accelerate.
Dialogue: 0,0:01:56.57,0:01:58.78,Default,,0000,0000,0000,,Now on to the final question:
Dialogue: 0,0:01:58.78,0:02:00.66,Default,,0000,0000,0000,,When you do get your bike moving,
Dialogue: 0,0:02:00.66,0:02:03.00,Default,,0000,0000,0000,,why does it go forward?
Dialogue: 0,0:02:03.00,0:02:05.00,Default,,0000,0000,0000,,According to Newton's Third Law, \Nfor every action,
Dialogue: 0,0:02:05.00,0:02:07.86,Default,,0000,0000,0000,,there is an equal and opposite reaction.
Dialogue: 0,0:02:07.86,0:02:12.29,Default,,0000,0000,0000,,To understand this, think about what \Nhappens when you drop a bouncy ball.
Dialogue: 0,0:02:12.29,0:02:13.95,Default,,0000,0000,0000,,As the bouncy ball hits the floor,
Dialogue: 0,0:02:13.95,0:02:15.82,Default,,0000,0000,0000,,it causes a downward force on the floor.
Dialogue: 0,0:02:15.82,0:02:17.88,Default,,0000,0000,0000,,This is the action.
Dialogue: 0,0:02:17.88,0:02:21.00,Default,,0000,0000,0000,,The floor reacts by pushing \Non the ball with the same force,
Dialogue: 0,0:02:21.00,0:02:24.00,Default,,0000,0000,0000,,but in the opposite direction, upward,
Dialogue: 0,0:02:24.00,0:02:27.00,Default,,0000,0000,0000,,causing it to bounce back up to you.
Dialogue: 0,0:02:27.00,0:02:29.00,Default,,0000,0000,0000,,Together, the floor and the ball form what's called
Dialogue: 0,0:02:29.00,0:02:32.00,Default,,0000,0000,0000,,the action/reaction pair. \NWhen it comes to your bicycle,
Dialogue: 0,0:02:32.00,0:02:35.57,Default,,0000,0000,0000,,it is a little more complicated. \NAs your bicycle wheels spin
Dialogue: 0,0:02:35.57,0:02:39.00,Default,,0000,0000,0000,,clockwise, the parts of each tire \Ntouching the ground
Dialogue: 0,0:02:39.00,0:02:41.00,Default,,0000,0000,0000,,push backwards against the Earth:
Dialogue: 0,0:02:41.00,0:02:45.00,Default,,0000,0000,0000,,the actions. The ground pushes \Nforward with the same force
Dialogue: 0,0:02:45.00,0:02:49.26,Default,,0000,0000,0000,,against each of your tires: the reactions.
Dialogue: 0,0:02:49.26,0:02:53.00,Default,,0000,0000,0000,,Since you have two bicycle tires, \Neach one forms an action/reaction pair
Dialogue: 0,0:02:53.00,0:02:56.55,Default,,0000,0000,0000,,with the ground. And since \Nthe Earth is really, really, really big
Dialogue: 0,0:02:56.55,0:02:59.00,Default,,0000,0000,0000,,compared to your bicycle, it barely moves
Dialogue: 0,0:02:59.00,0:03:02.00,Default,,0000,0000,0000,,from the force caused by your bicycle \Ntires pushing backwards,
Dialogue: 0,0:03:02.00,0:03:11.80,Default,,0000,0000,0000,,but you are propelled forward.