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Dynamics Dynamics
The study of forces and energies
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 !
How Do We Represent Forces?
Force = 100 N to the right
SI unit for force is NEWTON
SI unit for force is NEWTON
How Do We Represent Forces?
Force = 200 N to the right
Effects Of A Force On Motion
Effects Of A Force On Motion
Change the size and shape of objects
Make stationary objects to
move
Change the speed of a
moving body
Cause a moving body to change its direction of motion
Resultant Of Two More Forces
Two or more forces on a body can be replaced by a single force called the resultant force.
8
2
0
to the right
to the right
Balanced Forces And Unbalanced Forces
Balanced – Zero resultant force Unbalanced – there is a resultant force
Free-Body Diagram
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.
When there is NO resultant force acting ona stationary object, it will remain at rest.
Total upward force equal to total downward force
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.
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 AccelerationF = ma
Friction
Friction is a force that opposes the sliding motion between two surfaces in contact with each other.
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.
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.
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 %.
Ways To Reduce Friction• Using ball bearings or wheels.• Using lubricants such as oil and grease.• Use highly polished surfaces for moving
parts.
Ways To Reduce Friction• Designing the shape of the vehicle to be
streamlined.• Use air-cushion.