Physics – Big Idea

Earth Moon

Per Randall Knight, Five Easy Lessons in Physics

Physics – Big Idea

Physics – Big Idea

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Physics – Big Idea

A scalar quantity is just a regular number.

It might have units. So your mass is a scalar (it might be 60 kg). The height of Mt. Everest is a scalar (8848 m). You

add, subtract, multiply, and divide scalars in the usual way you’re used to.

A vector quantity has both a magnitude (or value) and a direction.

Your velocity is a vector (it might be 15 m/s towards the east). Forces are vectors (I’m pushing towards you with 50 N of force). You add and subtract vectors using

the parallelogram or tip-to-tail method.

Physics – Big Idea

Physics – Big Idea

Physics – Big Idea

Once upon a time, long ago, you learned that

distance is rate times time

That’s fine, but now you know better.

If an object is speeding up, it goes even farther than you’d predict with that old equation. If an object is slowing

down, it goes less far than you’d predict.

The kinematic equations of motion describe this idea in the language of algebra. The parabola-shaped position vs.

time graphs describe the same idea in the language of analytic geometry.

Physics – Big Idea

Physics – Big Idea

Some tips for solving kinematics problems

1. Read the problem carefully – draw a SKETCH of the situation if it will help you with visualization.

2. Identify the kinematic quantities you KNOW values for. For instance, if a ball is ‘dropped’ then its initial velocity is zero, and its acceleration is 10 m/s2 downward.

3. Identify the kinematic quantities that are UNKNOWN. If you don’t know how long something dropped for, then Δt is unknown.

4. Use your list of KNOWNS and UNKNOWNS to choose an appropriate kinematic equation.

5. Don’t get in the habit of “equation hunting” – instead, develop FLUENCY by practicing with a huge variety of problems – graphing, drawing, calculating, writing, … exploring from every angle.

Physics – Big Idea