here are the physics lecture

1. Lecture 1: Forces
General Physics 1

2. Learning Outcomes:
At the end of this section, you’ll be able to:
• understand what a force is.
• describe some types of forces
• Treat bodies as point particles.
• Construct and interpret free-body force diagrams.
• Apply the equilibrium condition, ΣF = 0.
• Understand and apply Newton’s three laws of motion.
• Solve problems involving solid friction.

4. What types of forces are there?

6. • In each of the four examples given, there is a change
in the motion of the object.
• The velocity of an object changes with time i.e.
there is acceleration.
• A force can cause an object to accelerate or
decelerate.

10. Newton’s first Law of
Motion is also known as
the Law of Inertia.

11. Unbalanced Forces and Newton’s Second Law
If the resultant force acting on an object is not zero, we say the forces are unbalanced.
Forces cause the book to accelerate or decelerate.

12. Unbalanced Forces and Newton’s Second Law
• Unbalanced forces causes an object to accelerate, decelerate or
change direction.
• The direction of acceleration is in the direction of
the resultant force.
Unbalanced forces and their relation to
Newton’s Second Law

19. The force that arises in any body when it is
stretched is called tension. A string that is
taut is said to be under tension. The tension
force is the result of electromagnetic
interactions between the molecules of the
material making up the string.

21. Normal reaction contact forces
If a body touches another body, there is a force of reaction or contact force
between the two bodies. This force is perpendicular to the surface of the body
exerting the force.

22. Drag forces are forces that oppose
the motion of a body through a fluid
(a gas or a liquid).
Typical examples are the air
resistance force experienced by a car
(Figure 2.31) or plane, or the
resistance force experienced by a
steel marble dropped into a jar of
honey.
Drag forces are directed opposite to
the velocity of the body and in
general depend on the speed and shape
of the body. The higher the speed,
the higher the drag force.

23. Upthrust
Any object placed in a fluid
experiences an upward force
called upthrust (Figure 2.32).
If the upthrust force equals
the weight of the body, the
body will float in the fluid.
If the upthrust is less than
the weight, the body will sink.
Upthrust is caused by the
pressure that the fluid exerts
on the body.

24. Frictional forces
Frictional forces generally oppose the motion of a body (Figure
2.33). These forces are also electromagnetic in origin.
Figure 2.33 Examples of frictional
forces, f. In (a) there is motion
to the right, which is opposed by a
single frictional force that will
eventually stop the body. In (b)
the force accelerating the body is
opposed by a frictional force. In
(c) the body does not move; but it
does have a tendency to move down
the plane and so a frictional force
directed up the plane opposes this
tendency, keeping the body in
equilibrium.

28. Friction that occurs between two bodies in
contact with one another while they are at
rest.
Its friction which prevents an object from
moving while it is still
Friction that opposes the movement of a body
which is already in motion.
Its friction that slows or stops an object from
moving.

30. Equilibrium
Equilibrium of a point particle means that the net force on the particle is
zero. The net force on a particle is the one single force whose effect is the
same as the combined effect of individual forces acting on the particle. We
denote it by ΣF. Finding the net force is easy when the forces are in the same
or opposite directions (Figure 2.43).