Transcript Newton`s First Law of Motion

Newton’s Laws of Motion
Forces cause changes in motion.
Newton’s Laws of Motion
Preliminary Question:
• What do all of the following have in common?
Galileo on Motion
• Once an object is moving, no
force is needed to keep it moving
• Only if friction is present, you
need to push something to keep
it moving
• Without friction, a moving object
keeps on moving at constant
velocity
Galileo on Motion
a. Ball rolls down - downward push (from gravity) –
speed up
b. Ball rolls upward - downward push (from gravity)
– slow down
c. Ball rolls on a level floor, the floor compensates
for gravity, no push – constant velocity
Galileo on Motion
Galileo stated:
Every object has this tendency to keep moving
without changing its motion if it was moving;
or to remain at rest if it was at rest
The property of a body to resist changes to its
state of motion is called inertia.
Mass – is a quantitative measure of an object’s
inertia
Our Experimental Evidence: Ball Lab
No push: ball rolls at
constant velocity
Yes - PUSH: balls ACCELERATE
Forces cause changes in motion.
Newton’s First Law of Motion: Inertia
• Every object continues in a state of rest, or of
uniform speed in a straight line, unless acted
on by a nonzero net force.
Simply put, things tend to keep on doing what they’re already
doing.
– Objects in a state of rest tend to remain at rest.
– Only a force will change that state.
Newton’s First Law of Motion: Inertia
Simply put, things tend to keep on doing what they’re already
doing.
Objects in a state of motion tend to remain in motion
with constant speed in a straight line.
Only a force will change that state.
Don’t let this be you. Wear your seat belt.
Because of inertia, objects (including you) resist changes in
their motion. When the car going 80 km/hour is stopped by
the brick wall, your body keeps moving at 80 km/hour.
Newton’s First Law of Motion
• Observe what happens to the crash dummies
in the video. Explain using Newton’s First Law.
• Crash Test
• Observe what happens to the curling stone in
the video. Explain using Newton’s First Law.
• curling
Newton’s First Law of Motion: Inertia
Newton’s First Law of Motion
• Cruising airliner moves at constant velocity
because all forces acting on it are balanced
Newton’s Laws of Motion
• All forces balance so the airliner
moves at constant velocity
• Unbalanced force from
the club accelerates the
golf ball