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level: 4-6

Questions and Answers List

level questions: 4-6

QuestionAnswer
resultant forcethe single force that has the same effect as all of the forces acting on an object
triangle of forcesa closed triangle drawn for an object in equilibrium. The sides of the triangle represent the forces in both magnitude and direction.
equilibriuman object in equilibrium is either at rest or travelling with a constant velocity because the resultant force on it is zero
components (of a vector)the magnitudes of a vector quantity in two perpendicular directions
resolving (the vector)to split a vector (such as a force) into two vectors at right angles
free-body force diagrama diagram showing all the forces acting on an object (but not the forces it exerts on other objects)
centre of gravitythe point where the entire weight of an object appears to act
moment of a forcethe product of the force and the perpendicular distance from the line of action of the force to the point
principle of momentsthe sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point provided the body is in equilibrium
couplea pair of equal and opposite forces that act on an object at different points and produce rotation only
torque (of a couple)the product of one of the forces and the perpendicular distance between the forces
energya calculated quantity that is conserved during any change; that which is transferred when a force does work
joulethe work done when a force of 1N moves a distance of 1m in the direction of the force
gravitational potential energy, Epthe energy a body has due to its position in a gravitational field
principle of conservation of energyenergy cannot be created or destroyed. It can only be changed from one form to another
powerrate at which a device does work per unit of time
wattone watt is one joule per second
workwhen a force moves (displaces) the body in the direction of the force; energy is then transferred from one body to another
potential energythe energy an object has because of its position or shape
linear momentumthe product of its mass and velocity
closed systema system of interacting objects in which there are no external forces
conservation of momentumthe sum or total momentum of the bodies in a closed system is constant provided no resultant external force acts
perfectly elastic (collision)the total kinetic energy of all the bodies remains constant
inelastic (collision)kinetic energy is not conserved; some is transferred to other forms such as heat
Newton's first law of motionan object remains at rest or travels at constant velocity unless it is acted on by a resultant force
Newton's second law of motionthe resultant force on a body is proportional (or equal) to the rate of change of momentum of the body
Newton's third law of motionwhen body A produces a force on body B then body B produces an equal and opposite force on body A