IB Physics Topic 2 Mechanics: The Study of Motion. Galileo (1564-1642)

Introduction to Mechanics.

1. In Physics, the study of motion is known as Mechanics. This is divided

into Kinematics, the study of HOW things move, and Dynamics, which is

concerned with WHY they move.

2. Galileo (1564-1642) was the first to study motion and developed

Kinematics. He performed his experiments Pisa, Italy, frequently dropping

objects from the Leaning Tower and/or rolling spheres along level surfaces

and down ramps.

Isaac Newton (1642-1727), a theoretical physicist, formulated Dynamics by

deriving his 3 Laws of Motion and the Law of Universal Gravitation. We will

study his work in depth later.

3. Galileo's study of motion produced four motion formulas: (I) Δs = vavg·Δt ,

with Δs = s - s0 , and vavg= (u + v)/2 , (II) v = u + a·Δt ,

(III) v2 = u2 + 2a·(Δs) , and (IV) s - s0 = u·t + ½a·(Δt)2 .

4. Instantaneous velocity can be computed by finding the slope of a tangent

line at any point on the graph of displacement as a function of time, or

v = Δs/Δt.

5. Instantaneous acceleration can be computed by finding the slope of a

tangent line at any point on the graph of velocity as a function of time, or

a = Δv/Δt.

6. Velocity and acceleration can also be evaluated using a much longer

method involving limits, or shorter using calculus.

7. Keep in mind that we are still concerned with vectors. Displacement,

velocity, and acceleration are all directed quantities. In the previous

chapter we were also working with another vector, force.

8. Displacement, velocity, and acceleration can all be demonstrated

graphically. For example, straight lines on a position-time graph indicate

constant velocity, determined by the slope.

9. The area under a velocity-time graph is displacement while the slope

of the graph indicates acceleration. The area under an acceleration-time

graph is the velocity.

10. The acceleration due to gravity is -9.80 m/s2 for Earth at sea level.

The negative direction is downward.

11. This is known as free-fall acceleration and is the same for all

objects regardless of mass near the surface of the Earth.

12. To solve a motion problem in Physics use these steps:

(i) read the problem and identify the given variables

(ii) determine what you are asked to solve for

(iii) find the correct motion formula to use

(iv) use algebra to isolate the unknown

(v) substitute-in the given information and simplify.