Motion Terms - Speed - Kinematics

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Average Speed - how much distance an object covers per unit time

Sheldon from the Big Bang explains physics

Why is Science Important? from Alom Shaha on Vimeo.

“The most incomprehensible thing about the world is that it is comprehensible.”

— Einstein

Unit I - Mechanics

Study of the relationship between force and motion

I. Kinematics

Mathematical methods of describing and predicting motion

Describe motion by using:

A) Average Speed

Average Speed of 120 miles per hour can also be written ... 120 miles/hour

per = divided by

Could mean travelled 120 miles in one hour, OR ... 60 miles in 1/2 hour (30 minutes), OR 15 miles in 7.5 minutes.

Avg. Speed - how much distance an object covers per unit time

1) Units: m/s, km/hour, miles/hour

Average Speed = Δd/Δt

Distance

(meter ≈ 1 yard)

(km ≈ .6 miles)

Time

seconds, minutes, hours

Ex 1

Given

An object travels 5 meters in 2 seconds.
Find: its speed.

↓

Speed = Δd/Δt
= 5 m / 2 sec

= 2.5 m/s

Ex 2

Given

An object moves at a rate of 3 m/s for 1.5 seconds.
Find: how far did the object move?

↓

Speed = Δd/Δt →
3 m/s = d / 1.5 sec

d = 4.5 m

Photos made by Eadweard Muybridge (1830-1904). Animation by User Waugsberg. Public Domain.

Ex 3

Given

An object moves at a rate of 4 m/s over a distance of 10 meters.
Find: how long did it take to travel that distance?

↓

Speed = d/t →
4 m/s = 10 m/t (Cross Multiply)

(4 m/s)t = 10 m (Divide by 4)

t = 2.5 seconds

B) Motion Plots

(a.k.a. Motion Diagrams)

Position vs. Time Plot

Speed from 0 to 2 seconds?

Speed = Δd/Δt
= 5 m / 2 sec

= 2 m/s

Speed from 2 to 4 seconds?

Speed = Δd/Δt
= 5 m / 2 sec

= 2 m/s

Speed from 4 to 6 seconds?

Speed = Δd/Δt
= 5 m / 2 sec

= 2 m/s

Does the object travel faster or slower from 6 to 8 seconds?

Slower Speed

(smaller change in d during the same time)

Compare speed from 6 to 8 sec with speed from 8 to 9 sec.

Same Speed, Same Slope

What kind of motion produced this plot?

Curved position vs time plot, steepening slope

Increasing Speed

Displacement

Equations

Displacement →