Newtons first law (also called the law of inertia) states that all objects in motion remain in moving unless acted on by another force, and same for nonmoving objects. Along with the next two laws you will learn about, this is something that will always be true in the physical world. This law in particular is the reason why a car coasting down a road will eventually stop if the accelerator isnt pressed (the force acting on it is called the frictional force). Next, well cover Newtons other 2 laws, which involve forces.
Inertial mass is the property of an object that determines its acceleration when it interacts with other objects or systems.
Gravitational mass is the property of an object that determines the magnitude of its gravitational force when it interacts with other objects or systems.
Inertial mass and gravitational mass are experimentally the same.
The net force on an object is the vector sum of the individual forces.
Contact forces result from the interaction of one object touching another (ultimate due to interatomic electric forces).
Newton's 1st Law of Motion
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On the other hand if we add a force of 5N to the left of an object and a force of 3N to the right of an object, the net force is the vector sum of those two, or 2N to the left. 0195
And we know how to add up vectors already. For vectors like the 5N and the 3N addition, we have 5 to the left, we line them up tip to tail so then we have 3 to the right and what we are left with is from the starting point of the first to the ending point of the last, that 2N. 0208
Okay, the balloons attached to the puck. If I put it on a surface and put it in motion, it continues in that state of motion until acted upon by a net force. 0278
That is what Newton's First Law is saying, an object in motion will continue in motion in its same state of motion unless there is a net force to change it. 0289
Now, an object at rest will remain at rest. We see that all the time. 0300
The objects in motion, though, are so much less obvious because its hard to find a frictionless environment here on Earth. 0307
Think of sliding a book across the floor. There is a net force on it at all times because of friction. 0314
To really see this, you either need to have something like that low friction puck or you need to go out into space. 0319
Throw a football through space. As it moves, it is going to keep moving forever and ever and ever in that straight line, constant velocity motion until its acted upon by a net force. 0325
Or it eventually runs into something. Another net force. 0335
All right. So static equilibrium. This is a special case where the net force on an object is 0 and its not moving. 0338
The object is at rest. We will revisit this concept a little bit further when we explore Newton's Second Law. 0348
We could also talk on the other hand about dynamic equilibrium. 0357
In that case the net force on an object is still equal to 0, but now the object is moving at constant velocity or acceleration is equal to 0. 0362
Again, in no net force, the object continues in its current state of motion. Very, very important concept. 0374
Now, inertia is the tendency of an object to resist a change in velocity. 0381
The measure of an objects inertia is its mass and we talked about this briefly previously, but mass has two aspects. 0387
Inertial mass is how hard it is to change an objects velocity. 0395
Gravitational mass is how strongly a gravitational field affects a mass, but for the purpose of physics and anywhere we have ever looked here, mass and inertia are going to be synonymous in this course. 0399
Gravitational mass and inertial mass in any experiment ever done and documented, performed and documented, they have always been the same. 0412
No theoretical reason why that is true, but experimentally, it always turns out that way. 0422
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