1. Factors that Affect a Force  While riding your bike, when would you find yourself pedaling really hard?  Some ideas: when you want to go faster, when you want ride uphill, when riding with an additional person aboard  Recall that your pedaling is the unbalanced force needed to set your bike into motion  Speed and Mass are two factors that can affect the amount of force you apply  For example, you may not pedal as hard when riding downhill because the force of gravity is at work  This affects your change in speed, known as acceleration  Speeding up is called positive acceleration  Slowing down is negative acceleration, or deceleration

2. What is Newton’s 2 nd Law of Motion  Newton’s 2 nd Law of motion explains the relationship between force, mass, and acceleration  Newton’s 2 nd Law states that an object acted upon by a force will accelerate in the direction of the force.  This means: –The greater the force, the greater the acceleration –The greater the mass, the more force needed to accelerate the object –If you want two objects of different masses to accelerate at the same rate, more force is required for the heavier object  You encounter Newton’s 2 nd Law everyday  Think of your favorite sport, and how Newton’s 2 nd Law may apply to a particular situation

3. Demonstrating Newton’s 2 nd Law:  In Figure A, only one person is pushing the girl on the swing  There is less force being applied here, so the girl does not accelerate as much  In figure B, two people are pushing the girl on the swing  There is more force being applied here, so there is greater acceleration  So as the force applied increases, the acceleration increases B. A.

4. Demonstrating Newton’s 2 nd Law:  In figure A, the boy is pushing only one girl, so he does not need to apply as much force to make her accelerate  In Figure B, the boy is now pushing two people on the swing, and has to use more force to get them to accelerate  So as mass increases, the force being applied must increase B. B..A.

5. Expressing Newton’s 2 nd Law Mathematically:  This relationship can be easily expressed by using a formula:  Force = Mass x Acceleration  Force is measured in newtons  Mass is measured in kilograms  Acceleration is measured in meters/sec/sec or m/s 2  This unit is used because acceleration simply means a change in speed (m/s) over time (s)  The superscript “2” is used instead of writing time twice

6. Triangle for Newton’s 2 nd Law: F M A X ÷ ÷

7. How much force is needed to accelerate a 20 kg boulder to 10 m/s 2 ?  Write the formula using the triangle  Substitute in  Show all work  Fill in your answer on the line Force = _________Newtons

8. 300 Newtons of force are applied to a 10 kg object. How much will the object accelerate?  Write the formula using the triangle  Substitute in  Show all work  Fill in your answer on the line Acceleration = _________ m/s 2