There are two types of forces: non-fundamental and fundamental. The four fundamental forces are gravitational, electromagnetic, strong nuclear, and weak nuclear. Gravitational force causes attraction between objects due to mass. Electromagnetic force causes attraction or repulsion between charged bodies. Strong nuclear force holds atomic nuclei together, while weak nuclear force plays a role in radioactive decay. Contact forces require direct physical contact while non-contact forces do not. Mass is a measure of matter and weight is the force on an object due to gravity, related by the equation W=mg, where W is weight, m is mass, and g is acceleration due to gravity.

1. The Nature of Force

2. Force
 A push or a pull exerted by one object on
another body.
 The effect of force is to tend to change the
state of motion of the body on which it acts.
 It is a vector quantity
 Represented by SI unit “N”

3. 2 General Types of Forces
 Non-fundamental Forces
 Ex. ordinary push and pull forces and friction
 Fundamental Forces
 Ex. Gravitational Force, Magnetic Force, Strong
Nuclear Force, and Weak Nuclear Force

4. The Fundamental Forces
 Gravitational Force
 The force of attraction
between objects by virtue
of their masses and is
responsible for weights of
the bodies on Earth as
well as the motion of the
planets

5.  Electromagnetic Force
 An attractive or repulsive force between
charged bodies

6.  Strong Nuclear Force
 A force that holds the
constituents of the
nucleus of an atom
together

7.  Weak Nuclear
Force
 Plays a role in
the radioactive
decay of some
nuclei

8. CONTACT AND NON-CONTACT
FORCES
 Contact forces- forces that result from direct
physical contact between two objects.
 Non-contact forces- forces that do not
involve direct physical contact

9. Mass versus Weight
 Mass- the quantity of matter a body contains
 A vector quantity
 SI unit “kg”
 Weight- the force on a body due to gravity
 A scalar quantity
 SI unit “N” for Newton
 Mass and Weight Relationship
 W=mg

10. Sample Problem
 Lynne has a mass of 100.0 kg on Earth. What is her weight on Earth? What
is her weight on the moon? What is her weight on the moon where the
acceleration due to gravity is 1/6 that of the Earth?
 Solutions:
 Given: m= 100 kg W=mg
 W=(100kg)(9.8m/s2)
 W= 980 N
 On the moon, her mass will not change but her weight will change
 W=(100kg)(9.8m/s2)
 W= 163 N
6

11. Practice exercise
 Andee has a mass of 68.5 kg on Earth. What is
his weight of Earth? What should his mass be in
order to have the same weight at the surface of
the moon?

12. That’s all for now. Thank you
for listening.