Free Fall and Newton’s Second Law October 22, 2015

Bell Work A car starts at a speed of 80 km/hr and comes to a stop. It has an acceleration of -1.5 km/hr/min. How long (hr) does it take for the car to stop? A dog accelerates at a rate of 0.5 m/s2 for 1.5 min. What is the change in velocity?

Agenda Bellwork Check homework Notes Handout new packet Start on Homework

Goals Define Free Fall Understand the relationship between force, mass and acceleration.

Q: If an apple falls from a tree, why does it accelerate? A falling object is affected by the pull of gravity We say the object is in “free fall” when only gravity is acting on it

Q: If an apple falls from a tree, why does it accelerate? Gravity is an unbalanced force acting on the object, causing the object to change it’s velocity Remember: If all forces are balanced (net force of 0 N) the object will not change speed or direction!

Q: If an apple falls from a tree, why does it accelerate? On Earth, the acceleration due to gravity (symbol g) is 9.8 m/s2

Q: We know Newton’s 1st Law (object in motion remains so at same speed and direction), so what is Newton’s 2nd Law? States: the unbalanced force acting on an object (to move it) equals the object’s mass times its acceleration Tells us how the unbalanced force will affect the movement of an object

Newton’s 2nd Law Formula: F = ma UNITS: before you can calculate you must have numbers with these units! F = Force in Newtons (N) m = mass in kilograms (kg) a = acceleration in m/s2 F m a

Newton’s 2nd Law The second law shows that acceleration and mass are inversely proportional to each other Inversely proportional means that if one value increases the other value will decrease, assuming everything else stays the same.

Newton’s Second Law

Practice Problem: A baseball accelerates downward at 9. 8 m/s2 Practice Problem: A baseball accelerates downward at 9.8 m/s2. If the gravitational force acting on the ball is 1.4 N, what is the mass of the ball? What are we given? Formula Work?

Newton’s 2nd Law Let’s take a look at the units… Kg*m s2 1 N = 1 kg*m/s2 A NEWTON is defined as the amount of force needed to move a 1 kg mass object at an acceleration of 1 m/s2 Kg*m s2 m

Homework Part one in the new packet