So what is a force?

A force is really just a push or a pull on an object. It occurs when two objects interact with each other. Forces can be contact forces, meaning that the objects have to actually touch. Or they can be at a distance, think along the lines of magnets or gravity. A force is still present but the objects are at a distance.

It helps most to think about forces in terms of balance. You might hear the terms balanced or unbalanced forces.

Just as with velocity, we split forces into dimensions. So we talk about vertical forces and horizontal forces. Forces that act in the vertical dimension and forces that act in the horizontal dimension.

When balanced forces act on an object, that object does not move. Imagine tug of war where both teams are pulling completely equally. The force to the left is the same as the force to the right. They cancel each other out. They’re balanced.

Unbalanced forces are forces that act on an object unequally. Imagine one tug of war team pulling with 70 N of force and the other team pulling with 40 N of force. They are unequal. They are unbalanced forces. The team pulling with more force will move the other team.

Let’s forget the math today and focus on Newton’s Laws.

Newton was a mathematician and physicist born in the 1600s. He existed, taught and studied well before many of our modern discoveries had been made, but his impacts are still felt today. Most importantly, for us, in this Laws of Motion.

There are 3 Laws of Motion. All have to do with force and how an object experiences force.

The First Law is commonly referred to as the Law of Inertia. This law states that an object at rest stays at rest unless acted upon by an outside force. An object in motion stays in motion unless acted upon by an outside force.

There are a few ways to interpret this → most simply, objects do not just spontaneously start moving. A force MUST be applied to them. If you ever see a ball start to roll, a book start to fall or a flag wave in the wind, it is because a force was applied.

Similarly, object do not just spontaneously stop moving. A ball will roll and roll across the ground until … it hits a wall. Or until … the force of friction slows it down.

Db Link:

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However, we don’t always just move objects at a parallel to the ground. More often than not, we move them at an angle. Think about your field goal kickers on a football field or a missile being launched. These objects move up, peak and then come down.

We say that they follow a trajectory. They exhibit parabolic motion. The objects peak and then they fall. They are projectiles.

There are many important things about this motion. First, lets focus on that angled launch. Remember how last time we had to pay careful attention to the phrasing of the problem? Was the initial velocity horizontal or vertical?

Last week we talked about initial horizontal velocity. Objects launched parallel to the ground. But this week the launch is at an angle and so the velocity can be split into horizontal and vertical components.

This is where geometry and trigonometry comes into play. Let’s imagine that a football is kicked at a 30 degree angle from the ground with an initial velocity of 28 m/s.

The initial velocity is 28 m/s at a 30 degree angle. Velocity is a vector. Direction matters and therefore we are able to split the velocity into horizontal and vertical components.