Analyzing motion of a projectile

[burt]

I am working on vector valued functions and I'm trying to solve a problem about analyzing the motion of a projectile. The problem is: .
When I look in the textbook at the example problem, it says . I'm not understanding where the assumption that comes from. Is anyone able to explain?

 

[Dr.Peterson]

That's something called gravity.

It's a vector that points downward (-j), and its magnitude is mg, based on Newton's F = ma.

Has your book said anything about the physics of projectiles, or does it assume you know the physics?

 

[burt]

That's something called gravity.

It's a vector that points downward (-j), and its magnitude is mg, based on Newton's F = ma.

Has your book said anything about the physics of projectiles, or does it assume you know the physics?

I think it's pretty much assuming you know the physics

 

[burt]

That's something called gravity.

is gravity the g or the J?

 

[burt]

That's something called gravity.

It's a vector that points downward (-j), and its magnitude is mg, based on Newton's F = ma.

Has your book said anything about the physics of projectiles, or does it assume you know the physics?

Oh - j is the standard basis vector in the down direction. mg is the magnitude and is made up of the mass times the constant acceleration of gravity. That is really just ma like force usually is equal to just with a direction. Is that right?

 

[topsquark]

That's something called gravity.

? Pet peeve alert!! Danger Will Robinson, danger!

To paraphrase
That's something called [math]\color{red}weight[/math].

Calling it gravity isn't really wrong, it's just not as accurate to my mind.

Danger over. ?

-Dan

 

[firemath]

? Pet peeve alert!! Danger Will Robinson, danger!

To paraphrase
That's something called [math]\color{red}weight[/math].

Calling it gravity isn't really wrong, it's just not as accurate to my mind.

Danger over. ?

-Dan

That was almost was dangerous as "pi, not pie!"

 

[Dr.Peterson]

Calling it gravity isn't really wrong, it's just not as accurate to my mind.

I was speaking of the phenomenon called gravity, not saying that the quantity (vector) is called gravity.

I think that's valid, isn't it?

Oh - j is the standard basis vector in the down direction. mg is the magnitude and is made up of the mass times the constant acceleration of gravity. That is really just ma like force usually is equal to just with a direction. Is that right?

Yes.

Specifically, this is a force vector (due to gravity). And g represents the acceleration due to gravity, which is a specific value of a.

Technically, Newton's second law is F = ma, where F and a are vectors. In this case, a = -gj.

 

[burt]

Thank you!

I was speaking of the phenomenon called gravity, not saying that the quantity (vector) is called gravity.

I think that's valid, isn't it?


Yes.

Specifically, this is a force vector (due to gravity). And g represents the acceleration due to gravity, which is a specific value of a.

Technically, Newton's second law is F = ma, where F and a are vectors. In this case, a = -gj.

Thank you!