Newton’s Second Law/Force Body Diagrams

By:Brian Kidawa

Chris Hayden

Shoeb Siddiqui

Mike Murphy

Terms

• Force-Agent that results in accelerating or deforming an object.

• Net Force-sum of all forces on an object

• gravity-Attraction between two masses according to their mass.(9.8 m/s)

• Weight-Force of gravity on an object

• Normal Force-Force perpendicular to surface.

• Acceleration-Change of velocity due to a force over time.

• Equilibrium-Net force on an object is zero.

Newton’s Second Law

• Newton’s Second Law states: acceleration of a body is directly proportional to the net force on it and inversely proportional to its mass.

• F=ma

Concepts

• Says that an unbalanced force causes a change on motion.

• Most familiar form of Newton’s Second Law is F=ma.

• If forces are unbalanced, acceleration occurs.

• An object has equilibrium when all forces cancel out.

Reality Check!

• Weapons (guns)

• Cars

• Solar System

• People on chairs

• Sports

Sample Problems

• If the mass of a crate is 100 kg and sliding friction is 250 N, what is the acceleration of the crate when the pulling force is 500 N?

• m=100 kg a=? Pf=500 N Ff=250 N

• Fnet=ma Fnet=500-250 250N

• 250 N=100kg * a a=2.5N/Kg

Sample Problems continued..

• An object of mass 70kg is accelerated by a force of 20 N. What’s is its acceleration?

• F=20 N m=70kg a=?

• 20 N= 70kg*a

• a=.29 N/Kg

Quiz

• A 75 kg person traveling at a constant velocity on ice skates experiences a force of 40 N. What is the person’s acceleration?

• answer:a=0 m/s/s • What is the mass of an object that is

accelerated at 25 m/s/s that is pushed with a force of 500 N.

• answer: m=20 kg

Quiz continued…

• A constant force acts on a 5 kg object and reduces its velocity from 7 m/s to 3 m/s in a time of 3 seconds. Find the amount of force acting on it.

• answer: F=6.65 N• A stock boy pushes a 20 kg box of SPAM with a force of

70 N and it accelerates at 0.4 m/s/s. Find the net force on the SPAM box.

• answer: 8N• A 60m kg man rides up in an elevator that is accelerating

at 0.8 m/s/s. What is the net force on the man?• answer: 48 N