Forces: Newton’s Second Law of Motion

Intro to Forces

○ Forces: ○ a push or pull that involves the interaction

between two or more objects ○ Vectors (they have magnitude and

direction) ○ There are 5 fundamental forces (gravity,

normal, air resistance, friction, applied) ○ can be represented by Free Body

Diagrams

Free Body Diagrams

Intro to Newton’s Second Law

○ How do the cheerleaders on the bottom get the cheerleader to fly through the air?

○ What would happen if they didn’t apply enough force?○  What would happen if they applied too much force? ○  Why do cheerleaders choose a lightweight person as a “flyer”? ○  Would the necessary force change if the “flyer” weighed more?

Isaac Newton’s Laws of Motion

○ Newton’s Second Law: Newton was able to not only describe the relationship between force, mass and acceleration; he discovered a simple formula that described the relationship numerically.  

For example: An object falling with an acceleration of 10 m/s2 with a mass of 10 kg is falling with a force of _____ Newtons

○ F= m x a

○ F =○ F =

10 kg 10 m/s2x

100 Newtons

Isaac Newton’s second law of motion: The Net Force acting on an

object are equal to the mass of the object times its acceleration.

FORCE IS A VECTOR!

Force is proportional to the mass and the acceleration. For example, if the acceleration increases, so will the Force.

Newtons (N) kg m/s2

Net force= sum of all the forces

Newton’s Second Law of Motion

Variable UnitForce Newtons (N) Mass Kilograms (kg), Grams

(g) Acceleration m/s2 

FAMx÷÷

Practice!

Force Mass Acceleration10 N 2 kg  20 N 2 kg  20 N 4 kg    2 kg 5 m/s2

10 N   10 m/s2

5 m/s2

10 m/s2

5 m/s2

10 N1 kg

YOUTUBE VIDEO

https://www.youtube.com/watch?v=ZvPrn3aBQG8

BELLRINGER: newton’s second law Roberto and Laura are studying across from each other at a wide table. Laura slides a 2.2 kg book toward Roberto. If the net force acting on the book is 1.6 N to the right, what is the book’s acceleration?

The net force of a golf cart is 390N north. If the cart has a total mass of 270 kg, what are the magnitude and the direction of the cart’s acceleration?

NET FORCES

Net Forces are the total amount of force acting on a object.

To find the Net Force, you add or subtract the total amount of Forces. Remember: Forces are vectors, so they can be negative!

NET FORCES

Forces are measured in Newtons

NET FORCES

Free Body Diagrams help us determine the presence of forces.

Forces can be balanced or unbalanced- Balanced Forces= Net Forces are equal to 0 and the

acceleration is 0- Unbalanced Forces= Net Forces are not equal to 0

BALANCED FORCES

BALANCED FORCES

UNBALANCED FORCES

UNBALANCED FORCES

BALANCED OR UNBALANCED?

BALANCED OR UNBALANCED?

BALANCED OR UNBALANCED?

example 1: net forces

WEIGHT= FORCE OF GRAVITY

example 2: What is the acceleration of a box weighing 666N if a force of 777N is applied to it?

EXAMPLE 3: What is the net Force of needed to accelerate a grocery sack (weighing 210 N) upward at 1.5 m/s2?

nEXT QUIZ ON FREE BODY DIAGRAMS & NEWTON’S 2ND LAW ON MONDAY, 11/19/18