Dynamics is the study of forces and energies. A force is a push or pull that has both a direction and magnitude. Forces can be represented as vectors and measured in Newtons. Forces can change the motion of objects by changing their speed or direction according to Newton's laws. Unbalanced forces cause changes in motion while balanced forces do not. Friction opposes motion between surfaces and can have both positive and negative effects that engineers aim to reduce.

1. Dynamics
The study of forces and energies

2. A force is a push or a pull that acts
on an object.
It has a specific direction.
It has a size or magnitude.
A force is a VECTOR !

3. How Do We Represent Forces?
Force = 100 N to the right
SI unit for force is
SI unit for force is
NEWTON
NEWTON

4. How Do We Represent Forces?
Force = 200 N to the right

5. Change the size and
shape of objects
Make Change the
stationary Effects Of A
Effects Of A speed of a
objects to Force On Motion
Force On Motion moving body
move
Cause a moving
body to change its
direction of motion

6. Resultant Of Two More Forces
Two or more forces on a body can be
replaced by a single force called the
resultant force.

7. 8
to the right
2
to the right
0

8. Balanced Forces And Unbalanced Forces
Balanced – Zero resultant force Unbalanced – there is a
resultant force

9. Free-Body Diagram

10. Newton’s First Law Of
Motion
Newton’s first law of motion states that an object
will remain in a state of rest or uniform motion in
a straight line unless acted upon by an external
force.

11. When there is NO resultant force acting on
a stationary object, it will remain at rest.
Total upward force equal to
total downward force

12. When there is NO resultant force acting on
an object moving with constant velocity, it
will continue to move that constant velocity
in a straight line.

13. Newton’s Second Law Of
Motion
Newton’s second law of motion states that the
net force acting upon an object is equal to the
product of the mass and acceleration of the
object.
Force = Mass x Acceleration
F = ma

14. Friction
Friction is a force that opposes the sliding
motion between two surfaces in contact
with each other.

15. Frictional Force
• Depends on the material in contact.
• Depends on the roughness of the surfaces.
• Is proportional to the force pressing the
surfaces together.
• Is independent of the area of contact.

16. Positive Effects Of Friction
• Enable us to walk without slipping.
• Used in brake pads to slow down
the motion of vehicles.
• To pick up things such as using
chopsticks to pick up food.

17. Negative Effects Of Friction
• Cause wear and tear of
moving parts in machines,
motors and engines.
• Reduce the efficiency of
engine power of cars by up to
20 %.

18. Ways To Reduce Friction
• Using ball bearings or wheels.
• Using lubricants such as oil and grease.
• Use highly polished surfaces for moving
parts.

19. Ways To Reduce Friction
• Designing the shape of the vehicle to be
streamlined.
• Use air-cushion.