PHYS 1510 Lecture Notes - Lecture 9: Net Force, Resultant Force, The Crate

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scarletsnake377

15 Oct 2018

School

York University

Department

Physics and Astronomy

Course

PHYS 1510

Professor

Ozzy Mermut

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Document Summary

Nuclear weak: electromagnetism (radioactive decay) f= m x a (inversely proportiante) a= f/m m= f/a. Dynmaics: the study of forces and their effects. Force of gravity is an attractive force between all objects and is represented by the symbol capital f arrow on top of capital f capital g. Normal force: the force perpindicular to surfaces in contact with each other; represented by the symbol capital f with arrow on top of capital f and capital n next to it. The force of riction is always parallel to the surface. Ff (arrow on capital f - vector) = friction force. Tension is a force exerted on objects acting away from the object being considered by pulling it. Forces can be either in contact or action-at-a-distance forces. Applied force= friction, air resitance (form of friciton?) Free body diagrams is useful to analyze situations and problems inlvolving forces.

Related Questions

Two dimensional dynamics often involves solving for two unknown quantities in two separate equations describing the total force. The block in (Figure 1) has a mass m=10kg and is being pulled by a force F on a table with coefficient of static friction

. Four forces act on it:

. The applied force FF (directed

above the horizontal).

. The force of gravity

(directly down, where

. The normal force N (directly up).

. The force of static friction fs (directly left, opposing any potential motion).

If we want to find the size of the necessary to just barely overcome static friction (in which case

, we use the condition that the sum of the forces in both directions must be 0. Using some basic trigonometry, we can write this condition out for the forces in both the horizontal and vertical directions, respectively, as:

In order to find the magnitude of force F, we have to solve a system of two equations with both F and the normal force NN unknown. Use the methods we have learned to find an expression for F in terms of

pucetiger860

This problem introduces the concept of tension. The example is a rope, oriented vertically, that is being pulled from both ends. Let F_u and F_d (with u for up and d for down) represent the magnitude of the forces acting on the top and bottom of the rope, respectively. Assume that the rope is massless so that its weight is negligible compared with the tension. (This is not a ridiculous approximation-modern rope material such as Kevlar can carry tensions thousands of times greater than the weight of tens of meters of such rope.)

Consider the three sections of rope labeled a, b, and c in the figure.

At point 1, a downward force of magnitude F_ad acts on section a.
At point 1, an upward force of magnitude F_bu acts on section b.
At point 1, the tension in the rope is T₁.
At point 2, a downward force of magnitude F_bd acts on section b.
At point 2, an upward force of magnitude F_cu acts on section c.
At point 2, the tension in the rope is T₂.

(A) What is the magnitude F_ad of the downward force on section a?

(B) What is the magnitude F_bu of the upward force on section b?

(C) The magnitude of the upward force on c, F_cu, and the magnitude of the downward force on b, F_bd, are equal because of which of Newton's laws?

(D) The magnitude of the force F_bu is ______ F_bd.

(E) Now consider the forces on the ends of the rope. What is the relationship between the magnitudes of these two forces?

(a) F_u > F_d

(b) F_u = F_d

(F) The ends of a massless rope are attached to two stationary objects (e.g., two trees or two cars) so that the rope makes a straight line. For this situation, which of the following statements are true?

(a) The tension in the rope is everywhere the same.

(b) The magnitudes of the forces exerted on the two objects by the rope are the same.

(d) The forces exerted on the two objects by the rope must be in the direction of the rope.

ambergiraffe181

1.A 4.00-kg block rests between the floor and a3.00-kg block asshown in the Figure. The 3.00-kg block is tied toa wall by ahorizontal rope. If the coefficient of static frictionis 0.800between each pair of surfaces in contact:

a) Draw free-body diagrams for the two boxesidentifying all ofthe forces acting on each of themasses.

b) Calculate the minimum force F that mustbe appliedhorizontally to the 4.00- kg block to make itmove?

c) What will be the tension in the rope underthe condition in(b).

2.Two skaters, a man and a woman,are standing on ice. Neglectany friction between the skate bladesand the ice. The woman pusheson the man with a certain force thatis parallel to the ground.

a) Must the man accelerate underthe action of this force? If so,what three factors determine themagnitude and direction of hisacceleration?

b) Is there a corresponding forceexerted on the woman? If so,where does itoriginate?

c) Is this force on the womanrelated to the magnitude anddirection of the force the womanexerts on the man? If so, how?

d) The mass of the man is 74 kgand that of the woman is 50 kg.The woman pushes on the man with aforce of 45 N due east. Determinethe acceleration (magnitude anddirection) of (i) the man and (ii)the woman

PHYS 1510 Lecture Notes - Lecture 9: Net Force, Resultant Force, The Crate

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