Newton S 2Nd Law Note Sheet

Newton’s 2nd Law – Note Sheet CP Physics

A ______is a push or a pull that is exerted on an object – causing its motion to change. There are two ways that an object’s motion can be changed – we can either change its ______or change its speed. In either case, what we are really changing is the object’s ______. Another name for a change in velocity is ______.

Newton’s 2nd Law takes into account the ______that is applied to an object and relates it to how the objects motion will change.

In words, Newton’s 2nd Law states that: When an ______force acts on an object, the object ______such that the product of the mass and the acceleration equal the unbalanced force.

What does that mean????? It is best re-written as a mathematical equation. Using the words from the definition above, we can re-write Newton’s 2nd Law another way. Since a product is found by ______two quantities, we must multiply the ______and the ______of an object and set it equal to the ______. This makes Newton’s 2nd Law read as: ______= ______

Before we continue any further, let’s see what we can tell about an objects motion just from this equation. First of all, we will assume that the mass of the object will always stay the same. As it is written, the equation is solved for ______. If the force on the object increased, and the mass remained unchanged, then the acceleration of the object would have to (increase/decrease) in order the maintain the equality. If both quantities increase, they are said to be ______proportional to one another. Notice that the quantities that are directly proportional are both ______and are on (the same/opposite) sides of the equation.

Now let’s solve the equation for acceleration. Written that way, the equation becomes ______. If we wanted to make a statement about how the mass and the acceleration are related, we would notice that acceleration is in the ______while mass is in the ______. This means that acceleration and mass are ______proportional to one another. In words that means if one of those quantities increases, the other quantity must (increase/decrease). Notice that acceleration is still (directly/inversely) proportional to the force. So, if we want an object to have a higher rate of acceleration we could either apply (more/less) force or (increase/decrease) its mass. It is also very important to note that the acceleration of the object is in the (same/opposite) direction as the force that causes the acceleration.

What are the UNITS of force?!?!?! There are actually two units for force. The SI unit for force is the ______(N) – named after Isaac Newton. This type of unit, which can be measured directly, is called a ______unit. We can also find the unit of force using the equation for Newton’s 2nd Law.

F = ma ______x ______= ______

When units are determined by deriving them from other measured quantities they are called ______units. So, the units for force can be written as either the fundamental unit ______or the derived unit ______.

Sample Problems: What is the net force required to accelerate a 1500-kg race car at 3 m/s2?

A cannon ball that has a mass of 55 kg if fired from a canon with a velocity of 770 m/s. The cannon barrel is 1.5 m long. What is the force on the canon ball while it is in the barrel?

Now is also a good time to differentiate between mass and weight. Mass is the quantity of ______in an object. Remember that mass is a ______quantity, since it is concerned only with magnitude and not ______. Another important difference between these two quantities is that the mass of an object (does/does not) change with the location of the object. In other words, if you had a mass of 50 kg on earth and you traveled to the moon, your mass when you reached the moon would be ______. There are two types of mass - ______and ______. We will mostly be concerned with the ______mass, which can be found by finding the amount of force needed to accelerate an object. To do this, we will use Newton’s (1st, 2nd, 3rd) law.

Weight is the force of a body of matter due to the gravitational attraction of some other body of matter – most commonly for us, this “other” body will be the ______. If there is no gravitational force present, an object (would still have/would not have) a weight. If the force of gravity in a location is different than it is on earth, then an object experiencing this new force of gravity would not have the same (mass/weight), but would have the same (mass/weight). Since weight is a force, it is a ______quantity and the units of weight are ______.

We can use Newton’s 2nd Law to find the weight of an object. However, to do so we will use special symbols. Since all objects accelerate towards earth because of gravity, we replace the “a” for acceleration in the equation with ______. The force of gravity is present whether an object is falling, resting on the ground, or being lifted. The force of gravity is called ______. In our equation, we can replace the “F” that represents force with ______(____).

Rewritten as the equation for weight, F = ma becomes ______= ______

Now do practice problems: page92, # 1-3 and page 94 #’s 5 - 7