Forces

Physics on the RoadLesson 10

Isaac Newton’s LawWe are learning

to…. understand that the

acceleration of something depends upon it’s mass and the resultant forces acting on it.

recall and use the formula

Force = mass x acceleration (F=ma) Investigate the effects

of an unbalanced force using equations of motion.

Linking force and motion

Philosophers and scientists have been linking force to motion since 300 B.C.Not always well.

Forces keep things moving

Aristotle 325 BC

Forces cause motion but are not needed to

keep them moving

Galileo 1630

Close but no cigar

Newton 1675

Newton’s Laws First Law

If there is no resultant force an object will remain at rest or if moving continue moving at a constant speed.

Second LawIf there is a resultant force an acceleration proportional to the force will occur.

InertiaReluctance to change speed.Depends upon mass.

Force = mass x acceleration

(N) (kg) (m/s2)

m x a

F

Calculation QuestionsF UNCAU

Q1. What force is needed to give the 800 kg drag car an acceleration of 5 m/s2?

Q2. A rocket has a mass of 5000 kg. It’s engines provides a force of 200 000 N. What is the rocket’s acceleration?

Wacky Race

Boeing 747Mass = 200 000 kgEngine Force = 500 000 N

Porsche 911Mass = 1500 kgEngine Force = 9000 N

Honda CBRMass = 200 kgEngine Force = 1600 N

m x a

F

a = F / m = 500000 / 200000 = 2.5 m/s2

a = F / m = 9000 / 1500 = 6 m/s2

a = F / m = 1600 / 200 = 8 m/s2

Forces cause acceleration

What can we vary?What will that vary?How should we measure this?

Experiment design

Can we measure the acceleration? Are there other measurements we

can make to calculate the acceleration?

Design your experiment and data table carefully.