# Primer

Created Thursday 05 May 2016

### Dimensions and Units

**Dimension**: Classification/nature of physical quantity

**Unit**: Standard of Measurement of a physical quantity

__Dimensional Homogeneity: You can only do mathematical equations on objects of the same size.__

### Models in Dynamics

Particle (Point) - has a mass, but a size that can be neglected; weight acts through center of mass.

Rigidbody - Can be considered as a combination of a large number of particles in which all the particles remain at a fixed distance from one another.

Real body - deformation is allowed (out of syllabus).

### Revision of Vectors

Like in vector math, displacement does not care about position - pretty basic, but it is **very important.**

Delta X or Dela Y is the average velocity in that direction. (For example, per second).

### Acceleration (and its misconceptions)

There is a difference between negative acceleration and deceleration.

Negative acceleration is acceleration in the negative direction as defined by the coordinate system.

Deceleration occurs when the acceleration is opposite in direction to the velocity (ie slowing down).

For example, if a car is moving in the negative direction and accelerating (ie going faster in the negative direction) , it would be not decelerating - it would be accelerating in the negative direction.

Negative acceleration does not necessarily mean the object is slowing down. If the acceleration and veclocity are both negative, the object is speeding up.

__tl;dr Deceleration is slowing down, which is not the same as negative acceleration.__

### Calculus

A note: Integration is incredibly important in Physics, probably even more so than differentiation.

Let's take the following equation:

a = dv/dt

__Integration of a will give you v, which will be the area under the curve in the graph.__

**Backlinks:**index:PHY200 Notes:Topics