If you're seeing this message, it means we're having trouble loading external resources on our website. If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. Newton’s first law of motion describes inertia. According to this law, a body at rest tends to stay at rest, and a body in motion tends to stay in motion, unless acted on by a net external force. Define the First Law of Motion
If you are ice skating, and you push yourself away from the side of the rink, according to Newton's first law you will continue all the way to the other side of the rink. But, this won't actually happen. Newton says that a body in motion will stay in motion until an outside force acts upon it. In this and most other real world cases, this outside force is friction. The friction between your ice skates and the ice is what causes you to slow down and eventually stop. Let's look at another situation. Refer to for this example. Why do we wear seat belts? Obviously, they're there to protect us from injury in case of a car accident. If a car is traveling at 60 mph, the driver is also traveling at 60 mph. When the car suddenly stops, an external force is applied to the car that causes it to slow down. But there is no force acting on the driver, so the driver continues to travel at 60 mph. The seat belt is there to counteract this and act as that external force to slow the driver down along with the car, preventing them from being harmed. Sometimes this first law of motion is referred to as the law of inertia. Inertia is the property of a body to remain at rest or to remain in motion with constant velocity. Some objects have more inertia than others because the inertia of an object is equivalent to its mass. This is why it is more difficult to change the direction of a boulder than a baseball.Doc Physics - Newton: Newton's first law is hugely counterintuitive. You may have learned it in gradeschool, though. Let's see it for the mind-blowing conclusion it really is. The second law states that the net force on an object is equal to the rate of change, or derivative, of its linear momentum. Define the Second Law of Motion
p=mv\text{p}=\text{mv}p=mv where, p=momentum\text{p} = \text{momentum}p=momentum ,m=mass\text{m}= \text{mass}m=mass , andv=velocity\text{v} = \text{velocity}v=velocity . From this equation, we see that objects with more mass will have more momentum. Picture two balls of different mass, traveling in the same direction at the same velocity. If they both collide with a wall at the same time, the heavier ball will exert a larger force on the wall. This concept, illustrated below, explains Newton's second law, which emphasizes the importance of force and motion, over velocity alone. It states: the net force on an object is equal to the rate of change of its linear momentum. From calculus we know that the rate of change is the same as a derivative. When we the linear momentum of an object we get:F=dpdtF=d(m⋅v)dt\displaystyle \text{F}=\frac{\text{dp}}{\text{dt}}\\\text{F}=\frac{\text{d}(\text{m}\cdot \text{v})}{\text{dt}}F=dtdpF=dtd(m⋅v) where, F = Force and t = time. From this we can further simplify the equation:F=md(v)dtF=m⋅a\displaystyle \text{F}=\text{m}\frac{\text{d}(\text{v})}{\text{dt}}\\\text{F}=\text{m} \cdot \text{a}F=mdtd(v)F=m⋅a where, a=acceleration\text{a} = \text{acceleration}a=acceleration . As we stated earlier, acceleration is the rate of change of velocity, or velocity divided by time.Newton's Three Laws of Mechanics - Second Law - Part 1: Here we'll see how many people can confuse your understanding of Newton's 2nd law of motion through oversight, sloppy language, or cruel intentions. Newton's Three Laws of Mechanics - Second Law - Part Two: Equilibrium is investigated and Newton's 1st law is seen as a special case of Newton's 2nd law! The third law of motion states that for every action, there is an equal and opposite reaction. Define the Third Law of Motion
FA=−FB\small{\rm{\text{F}_\text{A}=-\text{F}_\text{B}}}FA=−FB In this example, FA is the action and FB is the reaction. You have undoubtedly witnessed this law of motion. For example, take a swimmer who uses her feet to push off the wall in order to gain speed. The more force she exerts on the wall, the harder she pushes off. This is because the wall exerts the same force on her that she forces on it. She pushes the wall in the direction behind her, therefore the wall will exert a force on her that is in the direction in front of her and propel her forward. Take as another example, the concept of thrust. When a rocket launches into outer space, it expels gas backward at a high velocity. The rocket exerts a large backward force on the gas, and the gas exerts and equal and opposite reaction force forward on the rocket, causing it to launch. This force is called thrust. Thrust is used in cars and planes as well.Newton's Third Law: The most fundamental statement of basic physical reality is also the most often misunderstood. As your mom if she's clear on Newton's Third. Then ask her why things can move if every force has a paired opposite force all the time, forever. CC licensed content, Shared previouslyCC licensed content, Specific attribution
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