Download Chapter 4

The Laws of Motion
Introduction

 http://www.biography.com/people/isaac-newton9422656 Newton
 http://www.biography.com/people/galileo9305220 Galileo
First Law of Motion

 An object in motion will stay in motion unless acted
on by an unbalanced force
 Will this occur forever? What forces act everyday?
 If forces acting on the object are balanced, then the
velocity of the object doesn’t change!
 Inertia- the tendency of an object to resist a change in
motion
 Examples?
 https://www.youtube.com/watch?v=VrWgDnkIjE8&lis
t=PL4EE139D689C7CD27&index=1
Second Law of Motion

 In the presence of a net force, an object experiences
an acceleration and it can be calculated as F=ma. It
can also be calculated a=F/m
 Force is measured by Newtons (N), mass is in
kilograms (kg), acceleration is m/s2
 Remember-acceleration is a vector so it has a
magnitude (quantity) and direction!
 https://www.youtube.com/watch?v=LBSMy8gBGA&list=PL4EE139D689C7CD27&index=
2
Gravity

 Gravity- is an attractive force between any two
objects that depends on the masses of the objects and
the distance between them. The force increases as
the mass of either object increases, or as the objects
move closer.
 There are 4 basic forces. They are
 Electromagnetic-electricity and magnetism, chemical
reactions
 Strong Nuclear Force
 Weak Nuclear Force
 Gravity
Force diagrams

Gravity (continued)

 The Law of Universal Gravitation- published by Newton
in 1687 states that the force of gravity can be calculated
between any two objects if their mass and distance
between them is known. It states:

F= G x m1m2

d2
 This is how Neptune’s location was predicted.
 This is on page 105 in your text book!!
 G stands for the gravitational constant, which here on
Earth is 9.8 m/s2Thanks to Cavendish for this!
 Moons gravitational constant is around 1.6 m/s2
 http://www.bozemanscience.com/ap-phys-045-gravitational-force
Gravitational
Acceleration

 By the 2nd law of motion, the gravitational force
exerted by Earth on a falling object is the mass
multiplied by the acceleration so:
 gravitational force (N)=mass(kg) x g (m/s2 )
 Free fall-when all forces due to gravity can be
ignored, the object is in free fall.
 The distance covered in free fall can be calculated by:
 D= at2

2
Weight

 Weight is the gravitational force exerted on an object.
 Can be calculated by:

Weight (N)=mass (kg) x g
 g=9.8m/s2 on Earth.
 What is your weight on the moon?
 Weight and mass are NOT the same! Weight is a
force and mass is a measure of the amount of matter
an object contains.
 https://www.youtube.com/watch?v=zSJVCZ2ba0&index=5&list=PL07249EFA9038FDC1
Projectile Motion

 Draw in notebook! The arrows show the direction of
movement!
 https://phet.colorado.edu/sims/projectilemotion/projectile-motion_en.html
Projectile motion

 Earth’s gravity causes thrown objects to follow a curved path. These
horizontal and vertical forces that cause the motion act independently
of each other.
(honors content)

Centripetal Force

 Centripetal force is the net force toward the center of
a curved path
 Examples? (Gravity can be a centripetal force!)
 Centripetal acceleration is acceleration toward the
center of a curved or circular path.
 What is velocity doing? Why?
Honors content

Third Law of Motion

 When one object exerts a force on a second object, the
second object exerts a force on the first that is equal
in strength and opposite in direction.
 Called action reaction pairs or interactive force pairs
 These forces DO NOT CANCEL EACH OTHER!
 This is because they are acting on different objects!
 Example: swimmer in water
Interactive Force Pairs

Tension Forces

Thrust and Drag

 https://www.youtube.com/watch?v=zSJVCZ2ba0&index=5&list=PL07249EFA9038FDC1
Momentum

 Momentum is a property of a moving object that is
related to how much force is needed to change its
motion.
 Calculated by: p=mv
 The Law of Conservation of Momentum- if a group
of objects exerts forces only on each other, their total
momentum doesn’t change
 Example: playing pool.
 http://www.bozemanscience.com/momentum
Sketch this coaster in your notes. Label all forces and physics
concepts on the coaster where they apply!

Describe the motion of
each line


 Add scenario to have students create graph