What is Force?
2.2 p. 32-38
Mr. Richter
Agenda
 Warm-Up
 Intro to Acceleration (to the hallway!)
 What is Acceleration?
 Notes:
 Definition of Acceleration
 Units of Acceleration (What Acceleration really is)
 Calculating Acceleration
 Review HW Problems
 Graphs of Acceleration (time Permitting)
Agenda Day 2 and 3
Tomorrow
Tuesday
 What is Force?
 Acceleration Lab
 Newton’s Second Law (N2L)
 Force and energy.
Objectives: We Will Be Able To…
 Define and calculate acceleration.
 Explain the relationship between force, mass, and
acceleration.
 Determine mass, acceleration or force given two of the
quantities.
Warm-Up:
1. Describe the motion of the
object in one complete
sentence.
2. Sketch the Position vs.
Time graph you think
describes the object
Speed
 To the right is a Velocity vs.
Time (VvT) graph of an
object that starts at the
origin.
Time
Let’s go to the Hallway!
Warm Up
Time
Position vs. Time
Position
Speed
Velocity vs. Time
Time
Acceleration
What is Acceleration?
 What comes to mind when I say the word acceleration?
 Discuss at your tables for 1 minute and then we will discuss
as a class.
Definition of Acceleration
 Your book:
 Acceleration is the rate at which your speed increases.
 Real definition:
 Acceleration is the rate of change of an object’s motion.
 What’s the difference?
 Both have indicate that a change in speed is acceleration.
 The real definition implies that a change of direction is also a
form of acceleration, even if speed does not change.
Units of Acceleration
 Acceleration is the rate of change of speed relative to time,
so the calculation looks something like:
 This means the units of acceleration are any unit of speed
divided by the unit of time it takes to change that speed.
 Can we think of some possible units of acceleration?
Units of Acceleration
 The most common unit of acceleration we will use in this
class is m/s2 (“meters per second squared”)
 If acceleration is the rate of change in velocity [m/s] relative
to time [s]…
 The units for acceleration are:
 But we really mean “meters per second per second”, or a
change in meters per second (velocity) every second (time).
 Therefore, 50 m/s2 really means a 50 m/s change in velocity
every second.
Units of Acceleration: Practice
30 km/h/sec
15 m/s2 (= 15 m/s/s)
An increase of
An increase of
 30 km/h after 1 second
 15 m/s after 1 second
 60 km/h after 2 seconds
 30 m/s after 2 seconds
 90 km/h after 3 seconds
 45 m/s after 3 seconds
 300 km/h after 10 seconds
 150 m/s after 10 seconds
 Put it in a complete
sentence.
 Put it in a complete
sentence.
Acceleration Graphics (p. 32)
Calculating Acceleration
Calculating Acceleration
 Speed is how fast position changes, or the change in position
divided by time.
 Acceleration is how fast speed changes, therefore:
 What if acceleration is negative?
 Slowing down as opposed to speeding up.
 Sometimes called deceleration.
Let’s Review Your Homework Problems
 Remember to use the 5-step approach.
1. Looking for?
2. Given.
3. Formula
4. Solve
5. Check
Homework
 p. 55 Section 2.2
 #3-6
What is Force?
Force
 Acceleration is the change in an object’s motion.
 To change an object’s motion, a force is needed.
 A force is any push or pull, or any action that has the ability
to change an object’s motion.
 It can either change the speed of an object.
 Or change an object’s direction.
Force, Mass and Acceleration
 Reminder: mass is the amount of matter (atoms) in an
object.
 The amount of force required to accelerate an object
depends on:
 the amount of mass an object has
 the rate of acceleration the object reaches
 The is the basis of Newton’s Second Law
Newton’s Second Law (N2L)
 Isaac Newton discovered that the amount of force required to
move an object is proportional to the amount of mass the
object has, and the amount of acceleration of the object.
 In other words:
F = ma
 force = mass*acceleration
 Your book:
Newtons: Units of Force
 Force = mass*acceleration

= [kg]*[m/s2]
 We’re too lazy to write this, so we use
Newtons to abbreviate.
 1 Newton [N]= 1 kg*m/s2
 Newtons are very small units of force.
 Mr. Richter has a mass of about 95 kg.
It takes 95 N of force for Mr. Richter to
accelerate at 1 m/s2
 Mass resists acceleration
 Force cause acceleration
Net Force
 The net force is another way
of saying the sum of all of the
forces acting on an object.
 If the forces are in the same
direction, they are added
together. If they are in
opposite directions, they are
subtracted.
Net Force and Acceleration
 If there is a net force acting on an object ,there is also an
acceleration.
 Similarly, if there is no net force acting on an object, then
there is no acceleration.
 NOTE: this is not the same as no speed.
 An object can still be moving even if it is not acceleration.
 Constant speed means no acceleration which means no net
force.
Calculations with N2L: Practice
 A car has a mass of 1,000 kg. If a net force of 2,000 N is
exerted on the car, what is its acceleration?
 2 m/s2
Force and Energy
 Force is the action through which
energy moves. Or:
 Forces are created every time there is a
difference in energy between a highenergy situation and a low-energy
situation.
 For an object to move from a high
energy situation to a low energy
situation, there must be a force acting
on the object.
 Think, what force moves a car from the
top of a hill to the bottom?
Wrap-Up: Did we meet our objectives?