Transcript Force, mass, and acceleration

Force, Mass, and Acceleration
Sir Isaac Newton discovered the link
Acceleration
• Acceleration- rate at which an
object’s speed changes
• Amount that speed increases
compared to how long it takes
• Acceleration = change in speed/
change in time
A = v2- v1/t2- t1
• Units
meters per second per second
m/sec2
• Deceleration- slowing down
(negative acceleration)
• Zero acceleration- object
moving at constant speed
• Acceleration of gravity- 9.8 m/s2
–Object in free- fall in a vacuum
• Different on the moon or different
planets
Speed vs. time graph
• Positive slope= positive
acceleration (speeding up)
• Negative slope = negative
acceleration (slowing down)
• No slope =no acceleration
(constant speed)
Newton’s Laws of Motion
1. An object at rest will remain at
rest unless acted on by an
unbalanced force. An object in
motion will continue with
constant speed and direction
unless acted on by an unbalanced
force.
– Things tend to keep doing what
they’re doing until a force is
applied
Newton’s Laws of Motion
2. The acceleration of an object is
directly proportional to the force
acting on it and inversely
proportional to its mass
–Force causes an object to
accelerate, while the object’s
mass resists acceleration
Newton’s Laws of Motion
3. Whenever one object exerts a
force on another, the second object
exerts and equal and opposite force
on the first
–For every action, there is an
equal and opposite reaction
–If you push on a wall, you feel
the wall pushing back on your
hand
Force
• Any action that has the ability to
change motion (push, pull, etc)
• Force doesn’t always change
motion (pushing down on a table)
Force
• Units
–Pounds (lbs)
–Newtons (N)
•4.48 newtons in a pound
The Newton
• 1 N = 1 kg x 1 m/s2
• A force of 1 newton causes a 1kilogram mass to have an
acceleration of 1 m/s2
Mass
• Amount of “stuff” or matter in
an object
• Resists the action of forces,
making objects harder to
accelerate
Weight vs. Mass
• Weight - force of gravity acting on
an object
–N or lbs
• Mass is independent of gravity
–2.2 lbs = 1 kg
–30 lb child has a mass of about
14 kg
• Units of force = lbs and N
• Units of Mass= kilograms (kg)
Newton’s 1st Law
• Thing tend to keep doing what
they’re doing unless acted upon
by an outside force
• Law of Inertia
• Inertia - property of an object to
resist changing its state of motion
• Big trucks have more inertia than
small cars
• Which is harder to push: a ball
with a mass of 1 kg or a ball
with a mass of 100 kg?
• Once started moving, which is
harder to stop?
Newton’s 2nd Law
• Force causes an object to
accelerate, while the object’s mass
resists acceleration
• Force causes acceleration
• Mass resists acceleration
• Acceleration = force/mass
a = F/m
a = acceleration
F = force (N)
m = mass (kg)
2
(m/s )
a = F/m
• Must be sure to have m/s2 for
acceleration
• Must have N for force
• Must have kg for mass
Balanced and Unbalanced Forces
• Net Force- total of all forces acting
on an object
• When forces are balanced- Net
force= 0
–Equilibrium = no change in
motion (object at rest stays at
rest, object in motion stays in
motion)
• For motion to change- forces
have to be unbalanced
• Force acting on one side of
objects has to be greater than
force acting on other side