Download force - Blass Wiki

Physics Unit Four
Forces that Affect Motion
Force
•
•
•
•
•
A push or a pull.
Measured in newtons with a spring scale.
1 newton (N) = 1 kg m/s2
An apple weighs about 1 newton.
Calculate your weight in newtons:
Weight in pounds = _____
2.2 lbs/kg
Mass in kg = _____ x 9.8m/s2 =
Weight in newtons _____ N
Forces that affect motion
• Fa Applied Force –a force exerted on an object
by other objects in it’s environment.
• Ff Frictional Force – a force that opposes
motion between the object and the surface it
rests upon
• Fg Gravitational Force – the force of attraction
between two objects with mass (ex. Between
an object and the Earth, for example)
• Fn Normal Force – the supportive force of the
surface an object rests upon. It is equal to the
force of gravity acting on the object.
Normal means “perpendicular”
If forces are balanced…
No Motion
No net (unbalance) forces.
Ff
Fn
Fg
Fn
Ff
Fg
If forces are balanced…
No Motion
• No net (unbalance) forces.
Fg
Fn
Fn
50N, up
Fg
50N, down
If forces are unbalanced…
Motion
• Net (unbalanced) force.
Fn
Fn
Fg
Direction of
motion
Fg
Direction of
motion
Force Equations
•
Acceleration
–
–
According to Newton’s 2nd Law of motion, the
acceleration of an object is equal to the net force
acting on it divided by the object’s mass
Formula:
A=F/m
–
–
Therefore, doubling the mass of an object cuts its
acceleration in half
The unit for acceleration is m/s2
Force Equations
• Force
– Force on an object is equal to its mass and
acceleration
– Formula:
F= m(a)
Force Equations
• Weight
– Weight is the force of gravity acting on an
object
– Formula:
W= m(g)
– The unit for weight is also newtons because it is
a force
Force Equations
• Momentum
– Momentum is the product of an object’s mass and its
velocity
– An object has a large momentum if the product of its
mass and velocity is large.
– Formula:
Momentum (P)=
– The unit for momentum is kg*m/s
m(v)