Equations of Motion: When to Use & Point Object Necessity

[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?

 

[Orodruin]

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.

 

[kay]

[Q

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.

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

 

[Orodruin]

The suvat equations are valid for situations with constant acceleration.

 

[kay]

The suvat equations are valid for situations with constant acceleration.

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

 

[SteamKing]

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

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.

 

[CWatters]

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

 

[HallsofIvy]

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

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.