Agenda for 4/21/14 Welcome back  Inertia Lab – go outside HW – Finish lab

Agenda for 4/21/16 Quizzes handed back tomorrow Newton’s 1st Law of Motion Notes HW – Acc/Dec, Newton’s 1st Law Worksheet

Newton’s First Law of Motion Unit 7 - Motion Newton’s First Law of Motion

What is a force? Force - PUSH or PULL that can start, stop or change the direction of an objects’ motion.

A spring scale is used to measure force.

Units for force Measured in _______________ Answer: Newtons (N) What are some forces acting on you right now? Gravity Air Pressure Friction

Balanced Forces and Unbalanced Forces Balanced Forces: Forces that are EQUAL in size but OPPOSITE in direction. NO Motion!

Balanced Forces and Unbalanced Forces Unbalanced Forces: Forces that are UNEQUAL in size. Motion! https://www.nbclearn.com/portal/site/learn/science-of-nfl-football

Newton’s First Law of Motion Sir Isaac Newton stated: “An object at rest will remain at rest AND an object in motion will remain in motion, until an unbalanced force (gravity, friction, wind resistance) is acted upon it”. Also known as  LAW OF INERTIA

What does this mean? Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force. If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving. It takes force to change the motion of an object.

Some Examples from Real Life A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

Two teams are playing tug of war Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

Newton’s First Law is also called the Law of Inertia Inertia: the tendency of an object to resist changes in its state of motion The First Law states that all objects have inertia. The more mass an object has, the more inertia it has (and the harder it is to change its motion).

1st Law Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!

1st Law Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force? It’s a force we sometimes cannot see – friction.

Friction Definition: Force that occurs when 2 substances rub together. http://www.nsf.gov/news/special_reports/olympics/curling.jsp

Friction! There are 3 main types of friction: Sliding friction: friction occurring by sliding motion. ex. ice skating Fluid friction: friction occurring through air or liquid. ex. sky diving Rolling: friction occurring by rolling motion. ex. bowling

In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever.

Newtons’s 1st Law and You Don’t let this be you. Wear seat belts. 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 m/hour.

Centripetal Force Centripetal Force - force that pushes or pulls an object into a circular path. Always directed towards center of the circular path.

Examples of Centripetal Force Swinging a piece of rope. Ferris Wheel, merry-go-round, tilt-a-whirl. https://www.youtube.com/watch?v=1gK5MWQ__Ns London Ferris Wheel