linear kinematics chapter 3. definition of kinematics kinematics is the description of motion....
TRANSCRIPT
Definition of Kinematics
β’ Kinematics is the description of motion. Motion is described using position, velocity and acceleration.
β’ Position, velocity and acceleration are all vector quantities.
Velocityβ’ Velocity is defined as the rate of change in position,
or the slope of the position β time graph. The units for velocity are m/s.
π=π π β ππ
Ξπ‘
πππππππ‘π¦=β πππ ππ‘πππβππππ
β’ If the slope is horizontal the velocity must be zero.
β’ If the slope is upward the velocity must be positive.
β’ If the slope is downward the velocity must be negative.
β’ Notice that point 1 has less slope than point 2 & 3, compare there velocities.
Taking a Derivative
β’ The process of evaluating the slope to get the rate of change is called taking a derivative.
β’ The rules for estimating velocity from position are:
1.If the slope is horizontal, the velocity is 0.2.If the slope is positive (up), the velocity is
positive.3.If the slope is negative (down), the velocity is
negative.
Accelerationβ’ Acceleration is defined as the rate of change in
velocity, or the slope of the velocity β time graph.β’ The units for acceleration are m/s2.
π΄=π π βπ π
Ξπ‘
π΄ππππππππ‘πππ=βπππππππ‘π¦βππππ
β’ If the slope of velocity is horizontal the acceleration must be zero.
β’ If the slope of velocity is upward the acceleration must be positive.
β’ If the slope of velocity is downward the acceleration must be negative.
Acceleration is the Derivative of Velocity
β’ The rules for estimating acceleration from velocity are:
1. If the slope of velocity is horizontal, the acceleration is 0.
2. If the slope of velocity is positive (up), the acceleration is positive.
3. If the slope of velocity is negative (down), the acceleration is negative.
Integrationβ’ Integration is the mathematical process of getting the
area underneath a curve.β’ Integration of acceleration gives the change in
velocity.β’ Integration of velocity gives the change in position.β’ The integral sign can be interpreted as get the area
underneath the curve.
πβ«π‘0
π‘1
π΄ππ‘
β«The change in velocity over the interval from t0 to t1 is equal to the area underneath the acceleration β time curve.
Integration of AccelerationThere are several methods of integration. Determining the area of a rectangle is one method of integration. Area = (Height Γ Width) + Initial Value
V = Height x Width
V = (2 m/s2)(2 s)
V = 4 m/s
Over the interval from t = 0 to t = 2 s the velocity must change by +4 m/s.
Area = 4 m/s, velocity changes by 4 m/s.
Integration of Acceleration
V = Height x Width
V = (β3 m/s2)(3 s)
V = β9 m/s
Over the interval from t = 2 to t = 5 s the velocity must change by β9 m/s.
Area = 9 m/s, velocity changes by 9 m/s.
Integration of Acceleration
V = Height x Width
V = (4 m/s2)(2 s)
V = 8 m/s
Over the interval from t = 5 to t = 7 s the velocity must change by +8 m/s.
Area = 8 m/s, velocity changes by 8 m/s.
Integration of VelocityThe integration of velocity gives the change in position.
P = Height x Width
P = (β3 m/s)(2 s)
P = β6 m
Over the interval from t = 0 to t = 2 s the position must change by β6 m.
Area = β6 m, position changes by β6 m.
Integration of VelocityThe integration of velocity gives the change in position.
P = Height x Width
P = (2 m/s)(3 s)
P = +6 m
Over the interval from t = 2 to t = 5 s the position must change by +6 m.
Area = +6 m, position changes by +6 m.
Integration of VelocityThe integration of velocity gives the change in position.
P = Height x Width
P = (β4 m/s)(3 s)
P = β12 m
Over the interval from t = 5 to t = 8 s the position must change by β12 m.
Area = β12 m, position changes by β12 m.
Evaluate slope to estimate velocity Evaluate area to estimate position
A zero for velocity is a local max or min in position
πππππππ‘π¦=β πππ ππ‘πππβππππ π=
π π β ππ
Ξπ‘=(B3 β B2)/0.1
Computing Velocity from Position in Excel
Excel Filename: Get Vel & Accel Data Set 1.xls
π΄=π π βπ π
Ξπ‘=(C4 β C3)/0.1
Computing Acceleration from Velocity in Excel
Excel Filename: Get Vel & Accel Data Set 1.xls
π΄ππππππππ‘πππ=βπππππππ‘π¦βππππ
Integration of Acceleration in Excel
βπ=β« π΄ππ‘π π βπ π=β« π΄Γππ‘
π π=β«(π΄Γππ‘)+ΒΏπ πΒΏVelocity Final = (Acceleration Time) + Velocity Initial
The general equation for integration is:
Area = (Height Width) + Initial Value
Integration of Acceleration in Excel
π π=β«(π΄Γππ‘)+ΒΏπ πΒΏArea = (Height Width) + Initial Value
=(D4 * 0.1) + E3
Integration of Velocity in Excel
β π=β«π ππ‘π π βπ π=β«π Γππ‘
π π=β«(π Γππ‘ )+ΒΏπ πΒΏPosition Final = (Velocity Time) + Position Initial
The general equation for integration is:
Area = (Height Width) + Initial Value
Integration of Velocity in Excel
π π=β«(π Γππ‘ )+ΒΏπ πΒΏArea = (Height Width) + Initial Value
=(E3 * 0.1) + F2