Key Terms
A speed and acceleration probe consists of 4 parameters: speed, acceleration, velocity, and instantaneous center of rotation. Each parameter is defined and described below.
- Speed
- The rate of motion of an object, or the magnitude of change of its position. Speed is a scalar quantity representing the distance (d) covered per unit of time (t) and is expressed as follows: s = d/t. Speed is measured using the same physical units of measurement as the velocity but unlike velocity, speed does not include an element of direction. Speed is thus the magnitude component of velocity.
- Velocity
- The rate at which the object changes its position. Velocity is a vector value that includes both a magnitude and a direction. Velocity is measured using the same physical units of measurement as speed (d/t dimensions).
- Acceleration
- The rate of change of velocity. Acceleration is a vector quantity with dimensions d/(t2). To accelerate an object is to change its velocity, which is accomplished by modifying either its speed or direction (ex: uniform circular motion) in relation to time.
- Instantaneous Center of Rotation
- The point about which a body rotates at any given time. The following example shows the rotation
of two particles (A and B), around a rotation point (C).
- In the left figure, the velocities of A and B are known and different. The position of the ICR is obtained by drawing the perpendicular to Velocity A through A and the perpendicular to Velocity B through B. The point at which these two dotted lines intersect is the instantaneous center of rotation.
- In the right figure, the velocities of A and B are perpendicular to the AB line and their magnitudes are known. The instantaneous center of rotation is the point at which the AB line intersects with the line joining the extremities of the vector.