dynamics Flashcards
Newton’s 1st Law of Motion
body stays at rest or continue to move at constant velocity unless a resultant force acts on it.
Newton’s 2nd Law of Motion
the rate of change of momentum of a body is directly proportional to the net force acting on it, and, the direction of momentum change is in the direction of the net force.
Newton’s 3rd Law of Motion
whenever a force acts on a body, an equal but oppositely directed force of the same kind acts on another body
characteristic of action-reaction pair
-same nature
-equal magnitude
-act along same line but opposite directions
-act on different bodies
linear momentum
product of the mass of an object and its velocity (p=mv)
force
is the rate of change of momentum of an object which is free to move, and acts in the direction of the change in momentum.
the Newton
is the SI unit of force. 1N is that force required to give a mass of 1kg an acceleration of 1m/s² in the direction of the force.
moment of a force
moment of a force about any point is the turning effect of a force which is equal to the product of the force and the perpendicular distance from that point to the line of action of the force. (moments = fd)
couple
consists of 2 forces of equal magnitude but acting in opposite directions whose lines of action are parallel but separate.
torque of a couple
is the turning effect of the couple. for 2 equal but opposite parallel forces, each of magnitude F, with their lines of action separated by a perpendicular distance, d, the magnitude of the turning effect of the couple is the product of F and d.
principle of moments
for a body to be in equilibrium, the sum of clockwise moments about any pivot must be equal to the sum of anti-clockwise moments about that same pivot.
equilibrium
an object which, under the action of a number of forces, remains at rest or moving with a constant velocity and if in rotation is rotating at constant angular velocity is said to be in equilibrium.
2 conditions for equilibrium
- algebraic vector sum of the forces acting on the object in any direction must be 0.
- algebraic vector sum of the moments of the forces in the object about any point must be 0.
mass
measure of a body’s resistance to change in velocity.
density
the mass per unit volume of a substance.
weight
force acting on a mass due to a gravitational field.
apparent weight
the normal contact force experienced by an object in contact with a surface.
impulse
the product of the average force acting on an object and the duration of time for which the force acts.
principle of conservation of linear momentum
the total linear momentum of a system will remain constant if no net external force acts on it.
isolated system
a system which has no external force and no external torque acting on it, and, has no transfer of mass in and out of it.
head-on collision
velocities of the colliding bodies are collinear both before and after impact
elastic collision
a collision in which the total KE of the colliding bodies is conserved before and after the collision. relative velocity of separation is equal to the velocity of the approach.
inelastic collision
total KE of the colliding bodies is NOT conserved before and after collision.
perfectly inelastic collision
total KE of the colliding bodies is NOT conserved before and after collision, and the colliding bodies stick together after collision.
