# Equations of motion

Tags:
1. Nov 29, 2014

### kay

When can we use the three equations of motion?
Also, Is it necessary for the body we are considering to be a point object?

2. Nov 29, 2014

### Orodruin

Staff Emeritus
What do you mean by "three equations of motion"? Equations of motion generally just refer to the equations that describe how a system evolves with time, it does not have to refer to a particular system and the equations will look different depending on the system.

3. Nov 30, 2014

### kay

[Q
I mean these:
v^2 = u^2 +2as
s = ut + 1/2 at^2
v= uat

4. Nov 30, 2014

### Orodruin

Staff Emeritus
The suvat equations are valid for situations with constant acceleration.

5. Dec 1, 2014

### kay

So there is no condition on the body, right? That the body has to be a point mass or something?

6. Dec 1, 2014

### SteamKing

Staff Emeritus
No, the SUVAT equations just relate position, velocity and acceleration. They work just a well for a barleycorn as the Queen Mary in that regard.

7. Dec 2, 2014

### CWatters

The SUVAT equations can be used to calculate instantaneous velocities but be careful if the problem asks about average velocity.

8. Dec 2, 2014

### HallsofIvy

No, it is not necessary for the body to be a point object- however, if it is not, the calculations are a bit harder- you will have to consider how the various parts of the body move relative to each other. If the object is flexible, that could be complicated! Even if the body is rigid, you would need to include possible rotation about the center of mass.