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Figure 3.8: Motion diagram and free-body diagram for a box being dragged to the right, by means of a string, across a flat surface. Step 4 - Compare and contrast the free-body diagrams you drew in steps 2 and 3. The free-body diagrams are quite different, with one having no forces and the other having four.
SH. 11 FORCES & NEWTON’S LAWS WORKSHEET 1. 1. e Physics pulls a wagon with a force of 80 N. a) What is the net force if the force of fr. ction between the wagon and the ground is 12 N?b) If she uses 80 N to pull the wagon through a mud puddle, and the net force on the wagon.
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- Concept of a Moment
- Moment of a Force
- Moment of a Force
- M=Fxd
- = - 375 #-in
- Sign Convention for Moments
- What is the moment at A for the Noodle Beam fixed at A and loaded by Force F at B?
- M= -Fy.x + Fx.y
- θF
- WITH A FORCE & A COUPLE
- FORCE SYSTEMS
- Sign convention for Forces
- Resolution of a Force – How to Apply cos and sin
- C = C cos β
body CG of the body Translation Translation & Rotation Rotation When the Force is applied at the CG When the Force is not applied at he CG When the Force is not applied at the CG, & the body is hinged at the CG Objective: To explain the concept of a Moment If a Force P is applied at the midpoint of the free, rigid, uniform object, it will slide the...
This tendency of a force to produce rotation about some point is called the Moment of a force Objective: Definition of Moment in Statics
F d The tendency of a force to produce rotation of a body about some reference axis or point is called the MOMENT OF A FORCE
Objective: An example to illustrate the definition of Moment in Statics Common Examples in the Application of the Concept of Moment Example One: Closing the Door Moment = Force x Perpendicular Distance = Fxd
Objective: To explain the concept of Moment in Statics with everyday examples
Clockwise negative Anti-clockwise positive - + Objective: To illustrate the sign conventions for Moment in Statics
A d M = - F d Objective: To illustrate that Moment is always Force x Distance, irrespective of the shape of the structure
According to Varignon’s Theorem, a Force can be resolved into its components and multiplied by the perpendicular distances for easy calculation of the Moment Objective: To explain Varignon’s Theorem Proof of Varignon’s Theorem A θ about A= F x d cosθ θ
d M about A= -F x d F x d θ cosθ =− F d cos θ − F d sin θ y x y d sinθ =− F cos θ . d cos θ
d Introduce two equal and opposite forces at (which does not alter the equilibrium of the structure) Replace the above two Forces with a Couple= F.d F Hence a Force can be replaced with an Equivalent Fore and a Couple at another point. Objective: To explain how a Force can be replaced by a Force and couple at another point d = d
Objective: To explain various types of Force systems which occur in Construction y Collinear Force System x z x y Coplanar Force System z y x Coplanar parallel y Coplanar Concurrent x z Noncoplanar parallel z
Forces towards right Positive Forces upward Positive
θ F sin F θ θ x cos θ cos θ sin θ θF cos θ θ θ F sin cos θ sin θ sin θ cos θ θF cos θ θ F sin θ
x β C = C sin = B cos δ x = sin δ y C By x B y R
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Whatever is done to one side of an equals sign must be done to the other also. Take, for example, the equation: a = b + c a is the subject. To make b the subject, one must look at what is done to b and do the inverse to both sides. In the above equation, c is added to b, so b is made the subject by subtracting c from both sides of the equals sign:
Identify/isolate body or object of interest. Draw a FBD (to identify all forces acting on body) Apply Newton’s Law #2 (find Fnet & do: Fnet=ma) To apply Newton’s Law #2: draw a coordinate system apply Newton’s Law #2 in the x and y directions. FNet= ma is a vector equation. It must be satisfied independently in the x and y directions.
12. A boy pulls a wagon with a force of 6 N east as another boy pushes it with a force of 4 N east. What is the net force? 13. Mr. Smith and his wife were trying to move their new chair. Mr. Smith pulls with a force of 30 N while Mrs. Smith pushes with a force of 25 N in the same direction.
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Acceleration is defined as the rate of change of velocity per unit time. From this definition, an equation can be written: a v u t. = acceleration in metres per second per second. (m s–2) = final velocity in metres per second (m s–1) = initial velocity in metres per second (m s–1) = time in seconds (s)
