Chapter 4

The Laws of Motion

http://

www.biography.com/people/isaac-newton-9422656 Newton

http://www.biography.com/people/galileo-9305220 Galileo

Introduction

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&list=PL4EE139D689C7CD27&index=1

First 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

Second Law of Motion

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

Gravity

Force diagrams

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

Gravity (continued)

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

Gravitational Acceleration

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=zSJ-VCZ2ba0&index=5&list=PL07249EFA9038FDC1

Weight

Draw in notebook! The arrows show the

direction of movement! https://

phet.colorado.edu/sims/projectile-motion/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.

Projectile motion

(honors content)

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?

Centripetal Force

Honors content

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

Third Law of Motion

Interactive Force Pairs

Tension Forces

https://www.youtube.com/watch?v=zSJ-

VCZ2ba0&index=5&list=PL07249EFA9038FDC1

Thrust and Drag

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

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