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The SI unit for acceleration is metre per second squared (m⋅s −2, ). For example, when a vehicle starts from a standstill (zero velocity, in an inertial frame of reference) and travels in a straight line at increasing speeds, it is accelerating in the direction of travel. If the vehicle turns, an acceleration occurs toward the new direction ...
This example neglects the effects of tire sliding, suspension dipping, real deflection of all ideally rigid mechanisms, etc. Another example of significant jerk, analogous to the first example, is the cutting of a rope with a particle on its end. Assume the particle is oscillating in a circular path with non-zero centripetal acceleration.
While acceleration is a vector quantity, g-force accelerations ("g-forces" for short) are often expressed as a scalar, based on the vector magnitude, with positive g-forces pointing downward (indicating upward acceleration), and negative g-forces pointing upward. Thus, a g-force is a vector of acceleration.
There are two main descriptions of motion: dynamics and kinematics.Dynamics is general, since the momenta, forces and energy of the particles are taken into account. In this instance, sometimes the term dynamics refers to the differential equations that the system satisfies (e.g., Newton's second law or Euler–Lagrange equations), and sometimes to the solutions to those equations.
Newton's laws are often stated in terms of point or particle masses, that is, bodies whose volume is negligible. This is a reasonable approximation for real bodies when the motion of internal parts can be neglected, and when the separation between bodies is much larger than the size of each.
To find an acceleration, consider the forces affecting each individual mass. Using Newton's second law (with a sign convention of >) derive a system of equations for the acceleration (a). As a sign convention, assume that a is positive when downward for and upward for .
For example, an object subjected to physical or proper acceleration a o will be seen by observers in a coordinate system undergoing constant acceleration a frame to have coordinate acceleration: =. Thus if the object is accelerating with the frame, observers fixed to the frame will see no acceleration at all.
The metre per second squared is the unit of acceleration in the International System of Units (SI). As a derived unit, it is composed from the SI base units of length, the metre, and time, the second.