# 2D Kinematics

1. Feb 23, 2004

### xXshortyXx

Hey every one,
This is my first post on the forums glad to know i have such smart people here who can help me when im stuck. right now im taking physics 12 in British columbia. For some reason im really having trouble grasping the topic of 2d kinematics. any pointers in helping me understand will be greatly apprecieated!

THX Paul

2. Feb 23, 2004

I've always thought the whole gist of the thing went something like "Left and right have nothing to do with up and down except for time, and if you find something that appears to have both, it won't after a sine or cosine."

3. Feb 24, 2004

### Tom McCurdy

Well what specifically are you having trouble with. Maybe give an example problem.

4. Feb 24, 2004

### nautica

With 2D kineamatics you must remember that the Y direction (up and Down) are only dependent on gravity and the range or X direction is only dependent on the intial velocity in that direction. The 2 forumulas should help.

X = r cos of the angle.
Y = r sin of the angle.

Always break these vectors down and then it is a plug and chug from then on.

Nautica

5. Feb 24, 2004

Er.. x is not necessarily paired with the cosine and y is not necessarily paired with the sine. It really depends on which angle you're talking about. Additionally, 2D kinematics is not limited to motion under the influence of Earth's gravity and really should be generalized beyond such a scenario.

It is good advice to always break 2D vectors into their 1D components, though, and you will do that with trig functions.

6. Feb 25, 2004

### nautica

If you will notice in my post I qualified my Y by saying it was up and down.

Nautica

7. Feb 25, 2004

Even so, y not always paired with the sine. Take, for instance, a swinging pendulum. The angle is usually taken to be between the y-axis and the rod. In such a case, the vertical is paired with the cosine.

I think it's better to just remember to separate components and to learn to choose the sine or cosine as appropriate.

8. Feb 25, 2004

### Tom McCurdy

2d Equations

Y=Voyt-.5gt^2
Vy=Voy-gt
Vy^2=Voy^2-2gy