Forces and motion

Newtons 1st, 2nd and 3rd laws

(and also Terminal Velocity, Weight, Gravity and resultant forces)

They're honestly easier than you think they are. The first thing to learn is what resultant force means. Resultant force is the same as NET force. NET force being the difference in opposite forces. So for example if I have 20 N to the left and 10N to the right then the resultant force is 10N to the left.

The first law just states that if there is no resultant force then the object will either remain traveling at a constant velocity or it will remain stationary.
The second law just talks about what the first law doesn't cover. It states that a resultant force can be calculated using the formula F=ma.
The third law doesn't seem to have any connection what so ever to the first two. It just says if Object A pushes on Object B then Object B will push back on Object A with an equal and opposite force. This is basically just saying that if I push on the wall, the wall pushes on me with an equal and opposite force. When I say opposite force I mean opposite direction. The way I understand this is that if the force was not equal there would be a resultant force meaning I would accelerate when I leant on the wall I would move into or away from the wall. This doesn't make sense right? So it has to be equal in order to make sense.

Next to weight and gravity. Weight is basically the amount of force your body exerts on the floor. So when people ask you what your weight is and you say 60kg, you're not actually giving them your weight, you're giving them your mass. So what is your weight then? Well you know how if you go to another planet like mars you get lighter? This is because that other planet has a weaker gravitational field then earth. Earths gravity is 10 N/kg (9.8 to be exact). This means that every kilogram of mass exerts a force of 10 Newtons on the earth. So if you weigh 60kg then your weight is actually 600N on earth (588N to be exact). There is a formula for this but you don't really need it, its weight = mass x gravity. So if gravity is 10 N/kg (on earth) and you're 70 kg then w = m x g  so 70 x 10 = 700 N.

Right. On to terminal velocity. This is where it gets fun. So the earth has an atmosphere full of air right? Well this air creates air resistance or drag that opposes motion. Well when something falls through this atmosphere of air as the object (say an apple) goes faster and faster (it accelerates) the force of air resistance on the object gets bigger and bigger until at a certain point the force of air resistance equals the weight of the object. And hey, look back to Newton's 2nd law of motion, when an object has no resultant force it travels at a constant speed (or remains stationary). This is what terminal velocity is, it's basically the limit to how fast an object can fall in an atmosphere. On the moon however, there is gravity but no air resistance so you can imagine what will happen, with no air resistance the objects (say a washing machine and a $2 coin) will fall and hit the ground at the same time!

I made a YouTube video explaining this that you can watch for further clarification if you want:

If you're confused or have a topic you'd like me to go over let me know in the comments!