PHY_10_V2_TG_Revision term 1 (1)

Mechanics

displacement, s [m]

displacement of a particle is the length and direction of a line drawn to the particle from the origin

velocity, v [m s^-1]

rate of change of position with time

speed, v [m s^-1]

rate of distance travelled along a path

acceleration, a [m s^-2]

rate of change of velocity with time

change in velocity / rate of change of velocity;

 per unit time / with time; 

(translational) equilibrium

a body in equilibrium has zero resultant force acting on it and therefore has zero acceleration

sum of the (net) forces acting is zero;

weight, W [N]

the weight of an object is the gravitational attraction of a massive body (eg Earth) for that object

conserved

any quantity which is conserved maintains a constant total value

• kinetic energy is conserved in elastic collisions
• total mechanical energy is conserved when friction is negligible and KE and PE are not changed to other forms (such as sound, internal energy)
• total mass is conserved in all non-relativistic situations
• total mass-energy is conserved in all situations

conservation of energy

appropriate statement of principle of conservation of energy;

e.g. “Energy can not be created or destroyed, it just changes form.”

Newton’s 1^st law

a body will remain at constant velocity unless a net force acts on it

Newton’s 2^nd law

the rate of change of momentum of a body is proportional to the net force acting on it

This simplifies to  when the mass of the body remains constant

Newton’s 3^rd law

when two bodies A and B interact the force that A exerts on B is equal and

opposite to the force that B exerts on A;

  or

when a force acts on a body, an equal an opposite force acts on another body

somewhere in the universe;

linear momentum, p [kg m s^-1]

the product of a body’s mass and its velocity (therefore momentum is a vector with the same direction as the velocity)

momentum is mass x velocity;

allow an equation, with symbols explained.

momentum is mass × velocity;

impulse, Δp [kg m s^-1] or [N s]

the change in momentum of a body,

impulse is force x time or change in momentum;

(impulse =) force x time for which force acts;

impulse is force × time  / change in momentum;

law of conservation of momentum

if the total external force acting upon a system is zero / for an isolated system;

the momentum of the system is constant;

(vector) sum/total of momenta is constant;

for isolated system;

if the net external force acting on a system is zero;

then the total momentum of the system is constant (or in any one direction, is

constant);

if the total (or net) external force acting on a system is zero / for an isolated system;

the momentum of the system is constant/momentum before collision equals momentum after collision;

if the net external force acting on a system is zero / for an isolated system of interacting

particles;

the momentum of the system is constant / momentum before collision equals momentum after collision;

for isolated/closed system;

 total momentum remains constant;

the momentum of a system (of interacting particles) is constant;

if no external force acts on system / net force on system is zero / isolated system;

work, W [J]

force × distance (moved) in the direction of the force

power

the rate of working / work time;

If equation is given, then symbols must be defined.

the rate of working /;

Ratio or rate must be clear.

kinetic energy, E_K [J]

the energy associated with a body because of its motion

potential energy, E_P [J]

the energy possessed by a system due to the relative positions of its component parts (ie due to the forces between the component parts)

elastic collision

a collision in which the total KE is conserved

(a collision in which) kinetic energy is not lost / kinetic energy is conserved;

inelastic collision

a collision in which some kinetic energy is transferred to other forms (eg internal energy, sound), therefore the total KE is less after the collision than before

gravitational field strength

g [N kg^-1]

force exerted per unit mass;

on a small / point mass;

the force exerted per unit mass;

on a point mass;

the force per unit mass;

exerted on a point/small mass;

test mass

a small mass which has a negligible effect on the gravitational field in which it is placed

gravitational potential energy

the work done to move a body from infinity to a point in a gravitational field

gravitational potential

U [J kg^-1]

the work done per kilogram to move a body from infinity to a point in a gravitational field

the work done per unit mass;

in bringing a small/point mass;

from infinity to the point (in the gravitational field);

the work done per unit mass;

in bringing a small/point mass from infinity to a point (in the gravitational field);

escape speed

speed of object at Earth’s surface;

so that it will escape from the gravitational field / travel to infinity;

speed (of object) at surface (of planet) / specified starting point;

  so that object may move to infinity / escape gravitational field of planet;