Transcript Newton`s First Law

So, what’s next?
 We’ve learned how things move (speed and
acceleration) in a 1 and 2-dimensional plane
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Now, we’ll learn what
makes them move.
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What causes things to
move?
What is force?
How do you measure
force?
Let’s learn from a toy car
 Hypothesize what will happen when:
1. The toy car is not pushed
2. The toy car is pushed
3. The toy car is pulled with a rubber band
(Remember to use the word force & motion in your hypotheses)
 Experiment
 Results
 Conclusion—explain what you saw.
 What had to happen for the car to move?
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Push on it or
Pull on it
Newton’s First Law
 Newton’s First Law is also known as the Law of Inertia
 The law states:
“A body at rest, tends to stay at rest; a body in motion tends to stay
in motion, until an external force is applied.”
 A force is a push or a pull
 It is a vector --> care about direction
 An external force means an outside force is being put on
the object
 Examples:
 pushing against a wall
 pulling a sled
 A headwind against an airplane
To simplify it…
 A body at rest… (not moving)
will continue not moving
 A body in motion (moving)
will continue moving
Who is this Newton guy anyway?
 Isaac Newton was born
on Christmas day of 1642
(died in 1727)
 He was the Einstein of the
1600s. At 24 years old,
Newton developed his
famous laws of motion,
replacing 2000 years of
thought.
 He also discovered gravity
 You will know his name so
well 
Equilibrium
 Objects move only if the net force is not zero.
 The sum of all forces acting on an object is called the net
force.
 When all the forces on an object balance out, the object is
in equilibrium.
 When an object is in equilibrium it means it will stay at a
constant velocity
 This is why it’s important to draw a picture! So we can
figure out what the net force is (forces are vectors so
direction is important!) These drawings are called freebody diagrams.
What is the net force
on a book with 30 N
of gravity pulling it
down and 10 N of air
resistance pushing it
up?
If only…
 Many physics concept and laws we learn assume an
ideal world.
 But sadly, we don’t live in an ideal world because there
are other things at work.
 Newton’s First Law says an object in motion will
continue in motion unless another force acts on it,
many times in real life that force is known as friction
 Friction is a force that stops an object from moving
 In physics, we are going to pretend we’re in an ideal
world and that there is no such thing as friction
Inertia  Eureka! video
 Inertia is an object’s “laziness” or
resistance to change in motion
 Inertia is determined by an object’s mass
 Mass is the amount of stuff in an object
and measured in grams, kilograms and
milligrams
 Mass is not weight
 More mass
 More inertia
more inertia!
more force
to change motion!
Newton’s First Law – Old School…
Now for the demos!!