Zusammenfassung der Ressource
P2 2 Forces (continued)
- Falling objects
- The weight of an object is the force of gravity on it.
As it is a force, weight is measured in newtons (N)
- The mass of an object is the quantity of matter
in it. Mass is measured in kilograms (kg)
- Bathroom and kitchen scales are misleading because
they claim to measure WEIGHT in the units of MASS
- The force of gravity on an object is the
gravitational field strength where the object is
- The unit of gravitational field strength
is newtons per kilogram N/kg
- The gravitational field strength on
Earth is approximately 10 N/kg
- The gravitational field strength on
the Moon is approximately one
sixth of that on Earth, so 1.6 N/kg
- weight (in newtons) = mass (in kilograms) x
gravitational field strength (in newtons per kilogram)
- W = mg
- Terminal velocity
- The terminal velocity of a falling object is the
maximum velocity it reaches when falling in a fluid
- "Fluid" means a liquid
or gas, including the air
- At terminal velocity, the forces
on the object are balanced
- "Balanced" means equal in
magnitude but opposite in direction
- Weight downwards equals the drag
force (or air resistance) upwards
- Drag force
increases
with speed
- Stretching and
squashing
- The extension of a spring is directly
proportional to the force applied to it, provided
the limit of proportionality is not exceeded
- When the limit of proportionality is exceeded,
the spring is permanently deformed and will
not return to its original length
- This is known as Hooke's Law
- Force applied (in newtons) = spring constant
(in newtons per metre) x extension (in metres)
- Extension is the difference
between the length of a
spring and its original length
- The spring constant is the force per
unit extension needed to stretch it
- F = ke