1st Law of MotionInertiaMotion doesn't change without an outside force.. |

2nd Law of MotionF = maThis explains how much a force will change the motion of an ojbect. |

3rd Law of MotionFor every action...the force will effect the motion of both of the objects |

2nd Law **F = ma**

You may be surprised to learn that Newton wasn't the genius

behind the law of inertia. But Newton himself wrote that he

was able to see so far only because he stood on "the

shoulders of Giants." And see far he did. Although the law of

inertia identified forces as the actions required to stop or

start motion, it didn't quantify those forces. Newton's second

law supplied the missing link by relating force to acceleration.

This is what it said:

behind the law of inertia. But Newton himself wrote that he

was able to see so far only because he stood on "the

shoulders of Giants." And see far he did. Although the law of

inertia identified forces as the actions required to stop or

start motion, it didn't quantify those forces. Newton's second

law supplied the missing link by relating force to acceleration.

This is what it said:

When a force acts on an object, the object accelerates in the direction of the force. If the mass of an object is held constant, increasing force will increase acceleration. If the force on an object remains constant, increasing mass will decrease acceleration. In other words, force and acceleration are directly proportional, while mass and acceleration are inversely proportional. |

Technically, Newton equated force to the differential

change in momentum per unit time. Momentum is a

characteristic of a moving body determined by the product

of the body's mass and velocity. To determine the

differential change in momentum per unit time, Newton

developed a new type of math -- differential calculus. His

original equation looked something like this:

change in momentum per unit time. Momentum is a

characteristic of a moving body determined by the product

of the body's mass and velocity. To determine the

differential change in momentum per unit time, Newton

developed a new type of math -- differential calculus. His

original equation looked something like this:

F = (m)(Δv/Δt) |

where the delta symbols signify change. Because

acceleration is defined as the instantaneous change in

velocity in an instant of time (Δv/Δt), the equation is

often rewritten as:

acceleration is defined as the instantaneous change in

velocity in an instant of time (Δv/Δt), the equation is

often rewritten as:

F = ma |

The equation form of Newton's second law allows us to

specify a unit of measurement for force. Because the

standard unit of mass is the kilogram (kg) and the

standard unit of acceleration is meters per second

squared (m/s2), the unit for force must be a product of the

two -- (kg)(m/s2). This is a little awkward, so scientists

decided to use a Newton as the official unit of force. One

Newton, or N, is equivalent to 1 kilogram-meter per

second squared. There are 4.448 N in 1 pound.

So what can you do with Newton's second law? As it turns

out, F = ma lets you quantify motion of every variety. Let's

say, for example, you want to calculate the acceleration of

the dog sled shown below.

specify a unit of measurement for force. Because the

standard unit of mass is the kilogram (kg) and the

standard unit of acceleration is meters per second

squared (m/s2), the unit for force must be a product of the

two -- (kg)(m/s2). This is a little awkward, so scientists

decided to use a Newton as the official unit of force. One

Newton, or N, is equivalent to 1 kilogram-meter per

second squared. There are 4.448 N in 1 pound.

So what can you do with Newton's second law? As it turns

out, F = ma lets you quantify motion of every variety. Let's

say, for example, you want to calculate the acceleration of

the dog sled shown below.

If you want to calculate the acceleration, first you need to modify the force equation to get a = F/m. When you plug in the numbers for force (100 N) and mass (50 kg), you find that the acceleration is 2 m/s2. |

Now let's say that the mass of the sled stays at 50 kg

and that another dog is added to the team. If we assume

the second dog pulls with the same force as the first (100

N), the total force would be 200 N and the acceleration

would be 4 m/s2.

and that another dog is added to the team. If we assume

the second dog pulls with the same force as the first (100

N), the total force would be 200 N and the acceleration

would be 4 m/s2.

Notice that doubling the force by adding another dog doubles the acceleration. Oppositely, doubling the mass to 100 kg would halve the acceleration to 2 m/s2. |

Finally, let's imagine that a second dog team is attached to

the sled so that it can pull in the opposite direction.

the sled so that it can pull in the opposite direction.

If two dogs are on each side, then the total force pulling to the left (200 N) balances the total force pulling to the right (200 N). That means the net force on the sled is zero, so the sled doesn’t move. |

This is important because Newton's second law is concerned

with net forces. We could rewrite the law to say: When a net

force acts on an object, the object accelerates in the direction

of the net force. Now imagine that one of the dogs on the left

breaks free and runs away. Suddenly, the force pulling to the

right is larger than the force pulling to the left, so the sled

accelerates to the right.

with net forces. We could rewrite the law to say: When a net

force acts on an object, the object accelerates in the direction

of the net force. Now imagine that one of the dogs on the left

breaks free and runs away. Suddenly, the force pulling to the

right is larger than the force pulling to the left, so the sled

accelerates to the right.