WHAT IS A FORCE?

BellringerHow would you describe friction to someone who didnt know that word?

What do you think the word Force means?

Agenda NOTES: Forces & Newtons LawsWhat is force?Net Force5 types of ForcesNewtons Laws of MotionWHAT IS A FORCE?A force is a push or a pull that causes an object to change its motion.

Forces can cause objects to accelerate:Slow DownSpeed UpChange Direction

Measuring ForcesThe unit used to measure force is the Newton (N).One Newton is to equal to the force that would give a mass of 1 kg an acceleration of 1 m/s each second.

Net ForcesNet force is the overall force acting on an object.Think about what the word net means (not like a fishing net). How can this help you remember what a net force is?Forces can be represented by arrows since they are vectors.

Force DiagramA force diagram shows all of the forces acting on an object.

Balanced ForcesWhen forces are balanced they have a net force of zero.No change in movement.

Net Force = 0 NUnbalanced ForcesWhen forces are unbalanced the net force is not zero.Causes movement

Net Force = 5 N to the rightForce Vectors Practice #1

Force Vectors Practice #2

Types of Forces5 Types of Forces to Know:FrictionGravityNormalAppliedTensionFRICTIONFRICTION is a force that opposes sliding between two surfaces.

The friction force on an object always points in a direction opposite to the relative motion of the object.

Brakes push against the wheels of a car or a match rubs against a strikepad.

12GRAVITYGRAVITY pulls objects towards one another.

Airplanes are pulled towards the ground and our planet is pulled towards the sun.

GravityGravity is what causes objects to have weight.Mass is the amount of matter in an object.Weight is the force of gravity acting on an object so it is actually a measure of force.

NORMALThe NORMAL FORCE is a push directed at right angles from the surfaces of the interacting objects.

The ground pushes up against our feet.

APPLIEDAPPLIED FORCES are when one object pushes another.

A batter pushes a baseball with his bat.

TensionTension force occurs when a non-slack rope, wire, cord or similar device pulls on another object. A string holds up a kilogram weight or a girl hangs from trapeze rings.

17Newtons Laws of MotionIn the 1600s, Isaac Newton invented 3 laws that describe how and why things move.

The 3 Laws:Law of InertiaLaw for Calculating Forces (F=ma)Law of Action and Reaction

Law of InertiaAn object at rest will stay at rest and an object in motion will stay in motion unless it is acted upon by an unbalanced force.

Objects only change their speed or direction when a force makes them.This tendency to resist change is called INERTIA.

Law for Calculating Forces (F=ma)Force = (mass)(acceleration)

More force causes more acceleration.More mass causes less acceleration.The heavier something is (more mass), the more force it takes to change its speed or direction.F=ma Example1st video clip: Willis McGahee 230 lbshttps://www.youtube.com/watch?v=8qNj6jUcPN82nd video clip: Brandon Jacobs 270 lbshttps://www.youtube.com/watch?v=1r3yuWcd6zkBoth running back will be hit by a safety while running full speed. Watch the difference.Use Newtons 2nd Law to explain why Brandon Jacobs didnt go down.

Calculating Forces Practice #1A car with a mass of 1200 kg accelerates at a rate of 3 m/s2. What is the net force acting on the car?

F = maF = (1200 kg)(3 m/s2)F = 3600 NCalculating Forces Practice #2What is the acceleration of a 1200 kg car acted upon by a net force of 250 N?

a = F/ma = 250 N / 1200 kga = 0.21 m/s2Calculating Weight on EarthRemember weight is the force due to gravity.Knowing this concept we are able to calculate weight using the acceleration due to gravity on Earth.What is the acceleration due to gravity on Earth?9.8 m/s2

Ex. Calculate the weight of a person on Earth with a mass of 520 kg.W = ma = (58 kg)(9.8 m/s2) = 568.4 NLAW OF EQUAL AND OPPOSITE FORCESFor every action, there is an equal and opposite reaction.In other words, whenever something gets pushed, it pushes back.

AssignmentsNewtons Laws and Forces Worksheet