 Newton’s Second Law can be expressed with an equation:  Which can be re-arranged to isolate Force like this:

 Force is measured in Newtons  A Newton = the amount of force needed to accelerate a 1 kilogram mass at a rate of 1 m/s 2  Since F = m. a  1 N = 1 kg. m/s 2

1. Describe the motion of the object this graph depicts 2. Using F = ma, calculate the mass of the object

1.Describe the motion of the object this graph depicts the object is accelerating 2. Using F = ma, calculate the mass of the object using rise/run: 3N-1N/3m/s 2 – 1m/s 2 = 1 kg

 If there is acceleration (speed up, slow down, change direction), there is an unbalanced force.  remember: another name for unbalanced force is net force

 Look at the relationship between force, mass, and acceleration in this equation:  To keep the same acceleration, what must force do if mass is increased?  force must increase just as much

 To be more specific:  If acceleration stays constant and the mass of the object doubles, what must the force be doing?  doubling

 We already know that the formula for the second law of motion is F = ma  We can use this formula to calculate the force of weight  Weight = mass x acceleration gravity

 It’s really, really important to remember:  a net force results in acceleration  BUT  no net force does not mean no motion – an object will move at a constant speed in a straight line with no net force!!!

 The force required to accelerate a 2 kg mass at 4 m/s 2 is  (a) 6N(b) 2N(c) 8N(d) 16N  Answer  The correct answer is 8N because F = ma and so F = (2 kg)(4 m/s 2 )

 What force will be needed to accelerate a 8kg mass at the same acceleration as a 4kg mass?  (a) the amount of force does not change  (b) the force needs to be 4x’s as much  (c) the force should double  (d) it will take half as much force  Answer  The correct answer is “the force should double” because the mass doubled while acceleration was held constant.

 A cart has a constant acceleration from rest. The force on the cart must be  (a) decreasing  (b) zero  (c) constant  (d) increasing  Answer  The correct answer is “constant” because a constant net force creates a constant acceleration.