Every Physics Law Explained in 11 Minutes · The Analyst
用生动例子讲解牛顿三大定律、万有引力、能量守恒等核心物理概念，适合练习英语听力与科学词汇。
Newton's first law of motion.
牛顿的第一运动定律。
Also known as the law of inertia, states that every object will remain at rest or in uniform motion in a straight line,
这也被称为惯性定律，其内容是：每一个物体都将保持静止状态，或者保持沿直线匀速运动的状态。
unless compelled to change its state by the action of an external force.
除非受到外力作用而被迫改变其状态。
A bike rolling down a hill will keep moving until it hits something, unless someone hits the brakes.
一辆从山坡上滚下来的自行车会一直继续滚动，直到撞到什么东西为止——除非有人踩刹车。
Every object in the universe acts like that.
宇宙中的每一个物体都是这样运动的。
Whether an object is stationary or is moving on a straight path, it will remain that way until something changes that fact.
无论一个物体是静止的，还是沿直线运动的，它都会保持这种状态，直到有某种因素改变了这一状态。
But the law assumes the lack of friction and other forces, such as air resistance.
但该法律假设不存在摩擦力以及其他外力（例如空气阻力）。
Newton's first law implies that a bike rolling down a hill will never stop moving unless something stops it.
牛顿第一定律表明：一辆沿着山坡滚下的自行车除非受到外力的阻碍，否则会一直持续运动下去。
That doesn't happen on Earth, even if it doesn't hit anything, or if someone doesn't hit the brakes.
在地球上，这种情况是不会发生的——即使物体没有撞到任何东西，或者司机没有踩刹车，这种情况也不会发生。
That's because the first law is only valid in a frictionless environment.
这是因为第一定律仅在没有摩擦的环境中才成立。
There are microscopic irregularities in objects, and friction happens when the surfaces of two objects move against each other and cause resistance due to the irregularities.
物体表面存在微观层面的不规则结构；当两个物体的表面相互接触并移动时，这些不规则结构会导致摩擦力，从而产生阻力。
Simply stated, rougher surfaces have more irregularities and will cause more friction when rubbed against other surfaces.
简单来说，表面越粗糙，其不规则程度就越高；当这些粗糙表面与其他表面相互摩擦时，所产生的摩擦力也会越大。
Meanwhile, smoother surfaces are less likely to produce lots of friction, but still have microscopic irregularities that can still produce friction.
与此同时，表面越光滑，产生的摩擦力就越小；不过这些表面上仍然存在微观不规则结构，这些结构仍可能引发摩擦。
Newton's second law of motion.
牛顿第二运动定律。
Newton's second law of motion in math terms is force equals the mass of an object multiplied by its acceleration,
用数学公式表示，牛顿第二运动定律为：力（F）等于物体的质量（m）乘以其加速度（a），即 F = m × a。
which is the rate at which the object picks up speed.
这就是物体加速的速度。
That means that the force a moving object produces depends on how heavy and fast it is picking up speed.
这意味着，运动物体所产生的力取决于其自身的重量以及加速的速度。
Similarly, the equation can be twisted to get the object's acceleration,
同样地，通过调整方程式也可以计算出物体的加速度。
which means that an object accelerates depending on how heavy it is and the force exerted on it.
这意味着物体的加速度取决于其自身的重量以及作用在其上的外力。
If you earn a grocery store with your mom and were asked to push the cart, when the cart is still empty,
如果你和妈妈一起去杂货店购物，别人让你推购物车，而当时购物车里还什么都没有……
it doesn't take too much effort to push it forward and allow it to pick up speed.
推动它前进并让它加速并不需要花费太多精力。
But as your mom puts more stuff in, the effort required for it to accelerate is now more significant.
不过，随着你妈妈往里面继续添加更多东西，要让这个系统加速所需的努力也就变得更大（或者说更加困难）了。
This explains why balls are more accessible to push than boulders.
这就解释了为什么球比巨石更容易被推动（即：球更容易被移动）。
At the same time, a moving object that's heavy and picking up speed rapidly can also produce more force,
同时，一个质量较大且正在快速加速的移动物体也会产生更大的作用力。
which is why a runaway truck is more dangerous than a runaway sedan.
这就是为什么失控的卡车比失控的轿车更加危险的原因。
But the same law also means that lighter objects can move faster than heavier objects when the same force is applied.
但同样的物理定律也意味着：当受到相同的力作用时，较轻的物体比较重的物体移动得更快。
So if you place a V6 engine inside a sedan,
那么，如果你将一台 V6 发动机安装在轿车内部的话……
it will move faster than a pickup truck with the same engine as long as all of the other variables are unchanged.
只要其他所有因素保持不变，它的行驶速度就会比搭载相同发动机的皮卡更快。
Newton's third law of motion.
牛顿第三运动定律。
This one can best be summed up with the saying, For every action, there's an equal and opposite reaction.
这句话最能概括这个现象：“每一个作用力，都会产生一个大小相等、方向相反的反作用力。
It sounds like karma, basically what goes around comes around, but that isn't entirely the case.
这听起来像是“因果报应”——也就是“种瓜得瓜，种豆得豆”的道理，但实际上并非完全如此。
According to Newton, when you move, there will always be an opposite reaction exerted by another object.
根据牛顿的理论，当你移动时，总会有另一个物体对你产生一个方向相反的力（即反作用力）。
The mere act of stepping on the floor already produces that reaction.
仅仅踏上地板这一简单动作，就已经引发了那种反应。
A step produces a force that is exerted on the floor.
当一个人迈出一步时，他的身体会对地面施加一个作用力。
Meanwhile, the floor exerts the same force back to our foot in the form of resistance,
与此同时，地板会以阻力的形式将同样的力反作用到我们的脚上。
allowing you to feel that bounce in your step.
这会让你走路时感到轻松愉快、充满活力。
If the floor doesn't produce the same reaction, you won't be able to move forward because your foot will only end up sinking.
如果地板无法产生同样的支撑效果（即无法让你的脚稳固地站在上面），你就无法继续前进了——因为你的脚只会不断地往下陷。
It's similar to the recoil from firing a gun.
这种情况类似于开枪时产生的后坐力。
When you pull the trigger, force is created to propel the bullet forward.
当你扣动扳机时，会产生一股力量，将子弹向前推进。
But the same force exerted on the bullet to propel it forward also pushes back, which causes the gun to recoil.
但是，推动子弹前进的同一股力量也会产生反向作用力，从而导致枪支后坐（即枪支向后移动）。