unit 4 dynamics Flashcards
force
a force is push or pull acting on the object
SI unit: newton (N)
measured by a spring balance
effects of a force on the motion of a body
1) change the direction of a moving object
2) increasing the speed of a moving object
3) decreasing the speed of a moving object
4) make a stationary object moving
balanced force
when forces acting in opposite directions have the same magnitude, they said to be balanced because the resultant force is zero
when a resultant force is zero
the object will remain stationary if it was stationary before.
the object will continue to move at a constant velocity if it was moving.
unbalanced force
when forces acting in opposite directions have different magnitude, they said to be unbalanced because the resultant force is not zero
when the resultant force acting on an object is not zero
the velocity of the object can change
the direction of the object can change
newton’s first law of motion
every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it
newton’s second law of motion
when a resultant force act on an object of a constant mass, the object will accelerate in the direction of the resultant force
newton’s second law explains the following observations
-the greater the resultant force , the larger the acceleration
-a resultant force will cause an object to change its velocity
-for a given resultant force , the greater the mass of an object , the smaller the acceleration experienced
newton’s third law
the forces are always produced in pairs with opposite directions and equal magnitude
newton’s third law shows 4 important characteristics
1) forces occurs in pairs - an action and a reaction forces
2) action and reaction forces are equal in magnitude
3) action and reaction forces acts in opposite direction
4) action and reaction forces act between two different objects
free body diagram
a free body diagram helps us visualize all the forces acting on an individual object to find the resultant force acting on it in a particular direction
friction
the contact force that opposed or tends to oppose motion between surfaces in contact
falling objects with air resistance
when an object falls in the air , two forces in opposite directions are acting on it:
1) a downward force of weight ( w = mg )
2)an upward force of air resistance
these two forces acting in opposite directions affect the resultant force acting on the falling object , which in turns affect its acceleration and velocity as it falls towards the ground
factors affecting the magnitude of air resistance
as the surface area increases , air resistance decreases
