Definitions 2: Forces, Dynamics, WEP Flashcards
Newton’s 1st Law Of Motion
An object continues to be in a state of rest or in motion with constant velocity unless acted upon by a resultant force.
Inertia
The resistance to change in the condition of rest or
motion of a body.
Mass
The property of the body that resists change in motion.
Weight
The force acting on it due to a gravitational field.
W=mg
Linear momentum
The product of a body’s mass and its velocity.
p=mv
Newton’s 2nd Law Of Motion
The rate of change of momentum of a body is directly proportional to the resultant force acting on it and takes place in the direction of the resultant force.
Force
The rate of change of momentum.
Weightlessness
The state where the body does not experience the effects of contact forces.
Impulse
The product of the force and the time duration of the impact.
Newton’s 3rd Law of Motion
When body A exerts a force on body B, force on body A is equal in magnitude to force on body B from A. Both forces are in opposite directions but of the same kind.
Principle of Conservation of Linear Momentum
The total linear momentum of a system remains constant provided that no resultant external force acts on the system.
Elastic collision
Collision in which no kinetic energy is lost.
Kinetic energy of colliding bodies is conserved.
Inelastic collision
Collision where kinetic energy is not conserved (more specifically kinetic energy is lost).
Perfectly inelastic collision
The colliding bodies will coalesce (stick) with one another
and move off with the same velocity.
1 N (newton)
The magnitude of force that accelerates a mass of 1kg at a rate of 1ms^(-1) in the direction of the force.
Field
A region of space within which a force is experienced by a particle as a result of the physical property such as mass or charge.
Centre of gravity
A single point where all the weight of a body seems to act.
Gravitational field strength
The gravitational force per unit mass acting on a point mass placed at that point.
Electric field
A region of space within which an electric force is experienced by a charge.
Electric field strength
The electric force per unit positive test charge acting on a point stationary charge placed at that point.
Hooke’s Law
States that the change in length x of a material is directly proportional to the force F applied on it, provided that the limit of proportionality is not exceeded.
F=kx
Static Friction
The frictional force that acts when there is no relative motion between 2 surfaces.
Kinetic Friction
The frictional force that acts when two surfaces slide against each other.
Pressure
The normal force acting per unit area.
Upthrust
The upward force exerted by a fluid on an object submerged fully or partially in the fluid due to the difference in pressure exerted by the fluid on the upper and lower surfaces of the object.
Moment of a force about a point
The product of the magnitude of the force and the perpendicular distance of the point from the line of action of the force.
moment = Fd
Torque of a Couple
The product of the magnitude of one of the forces and the perpendicular distance between the lines of action of the forces.
Principle of Moments
States that when a body is in rotational equilibrium, the sum of clockwise moments about any point must be equal to the sum of anticlockwise moments about the same point.
Work done
Work done by a force is the product of the force and the distance moved in the direction of the force.
Kinetic energy
Kinetic Energy is the energy possessed by a body due to its motion speed.
Gravitational Potential Energy
Gravitational Potential Energy is the energy of a mass due to its position in a gravitational field.
GPE=mgh
Elastic potential Energy
Elastic potential energy is the ability to do work by the object when it is deformed, eg compressed or stretched.
EPE = 0.5kx^2
Law of Conservation of Energy
Energy can be converted from one form to another but it cannot be created or destroyed. The total energy of an isolated system is always constant.
Power
The rate of work done.
Efficiency
Useful work done by energy input / power output by power input (in percentage)
