The document discusses various forces, including weight, normal force, and tension, emphasizing the relationship between mass and weight through the equation w=mg. It details key concepts such as friction, stability, and equilibrium in terms of forces and torques acting on objects. Additionally, it introduces Newton's first law, stating that an object remains at rest or in uniform motion unless acted upon by a net force.

1. Force

2. Kinds of force
Weight/gravity
Normal force/supporting force/
contact force
Tension
Friction
Air resistance
upthrust

3. Mass
Mass is the property of a
body which resists
change in motion.

4. Weight
Weight is the force on the
object due to gravitational
field.
Relationship : W=mg
The gravity of the 1kg mass about
9.81N

5. Definition
Kind of
quantity
Variation
Mass Property Scalar
To the same
object—no
change
Weight Force Vector
Change with
position (planet
/ latitude/height)
Apparent weight

6. Center of mass/gravity
Regular shape
In the geometrical center.
Irregular shape
We can find it with a plumb line.
Page 76.
Gravity
It’s the point through which the
whole weight of the object seems
to act.

7. Stretching a spring
The spring follow F=kx
k is the constant of the spring
The extension is directly
proportional to the
tension /stretching force.
Within the elastic limit/ limit
of proportionality
Tension

8. Newton’ first law
A body continues in a state of rest
or of uniform motion in a straight
line unless acted upon by a non-
zero resultant force
A object keeps on moving with a
constant velocity or at rest unless
there is a net force acts on it.

9. friction
Static friction

10. Static friction force = net force tend to move
object
Direction of the friction is opposite to the
relative direction of the motion of the object.
F
A B C D

11. Sliding friction: f=μN
μ is a frictional constant
N is normal force.

12. Stability
Two conditions to be more stable
A lower center of mass
A wider base
Gravity

13. Moment/torque
Moment=force×?distace
Moment is the product of
force and the perpendicular
distance from the force to
the pivot.
Tuning
force

14. Conditions for object in
equilibrium
Net force in any direction is
zero.
Resultant moment to any
pivot is zero.
Tuning
effect