Transcript Newton`s 1 st Law of Motion

Motion and Forces
 All motion happens because there is a force.
 Newton’s Laws describe the relationship between
motion and force.
Forces
 Forces are anything that make an object start
moving or make an object slow down or stop.
 There are balanced and unbalanced forces.
 Unbalanced forces make an object start moving or
they make an object speed up or slow down if it is
already moving.
 Balanced forces mean that an object is at rest or
that it has a constant speed.
Newton’s
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Law of Motion
 If you slide your book across a carpeted floor, it
will eventually stop.
 Any ideas why?
 What about if you slide a book across a surface like
ice?
 FRICTION!!!!
Newton’s
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Law of Motion
 Newton’s 1st Law of Motion states: “An object at
rest will remain at rest and an object in motion will
remain in motion unless acted on by an
unbalanced force.
 Why do you think there are seatbelts in cars?
 http://teachertech.rice.edu/Participants/louviere/
Newton/carandwall.gif
Newton’s
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Law of Motion
 Inertia is the tendency of an object at rest to
remain at rest or an object in motion to continue in
motion.
 All objects resist changes in motion, so all objects
have inertia.
 Newton’s 1st Law is also called the “Law of Inertia”
Newton’s
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Law of Motion
 Mass is a measure of inertia.
 An object with a small mass has less inertia than
an object with a large mass.
 Therefore, it is easier to move an object with a
small mass.
 Ex. It is easy to hit a baseball with a bat and send it
flying in the air, but it is hard to do the same with a
bowling ball.
Mass vs. Weight
 All objects have mass.
 Mass is the amount of matter an object has.
 Weight is a measure of the gravitational force that is
exerted on an object.
 Remember that on Earth gravity is different than in
space or on other planets (related to Earth’s size)
 All objects feel a pull towards the center of the Earth
which is why all objects fall downward at a rate of
9.8 m/s2 (constant rate that never changes!)
Mass vs. Weight
 Even though your weight might be different, your mass
will still be the same (what you are made of does not
change!)
 To calculate “true” weight, you must use the
gravitational constant 9.8 m/s2 in the formula W=mg
 W=weight (Newton, N)
 M=Mass
(Kilogram, kg)
 G=Gravity (Same as acceleration, m/s2 )
Newton’s
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Law Video Clip
 http://www.youtube.com/watch?v=tbpqRSip4to
 http://www.youtube.com/watch?v=7702nTbov9c&feat
ure=related
Mass vs. Weight Practice
 Note: 1kg. =2.2 lbs
 To calculate your “true” weight, you would divide your
weight in pounds by 2.2kg.
 150 lbs/2.2 kg/lbs=68.18 kg
 Suppose you wanted to convert your weight from kg to
pounds. You would simply multiply your weight by 2.2
kg.
 75kg x 2.2= 165 pounds