Remember that if you choose a point where a force acts then that force has zero torque about that point. You should see if you can find some special point which would simplify your torque calculation. Design a Strategy: System: Choose the foot as the system noting that the tibia bone and the Achilles tendon are not part of the system. Forces: There are three forces acting on the foot. The normal force of the floor acts on the foot. You can actually determine the normal force by considering the entire body.
The Achilles tendon exerts a force of unknown! T but at a known angle! The problem states that you can ignore the weight of the foot. The condition Equation 2.
Then Equation 2. Note that the force F that the tibia exerts on the ankle will make no contribution to the torque about this point S. The torque diagram on the ankle is shown below. We shall first calculate the torque due to the Achilles tendon. The first thing to notice is! Therefore the magnitude of the torque is just the magnitude of the!
The direction of the torque is into the plane of the page in! The torque due to the force of the tendon T on the ankle about the point where the tibia exerts a force on the foot is then! We can now solve for the angle! Rewrite the two force equations Equations 2. T cos " Now take the inverse cotangent to solve for the angle! We can now use the horizontal force Equation 2. The mass of the ladder is ml , uniformly distributed.
The ladder is initially inclined at an angle! In this problem you will try to find the minimum coefficient of friction between the ladder and the floor so that the person and ladder do not slip. Problem 3 Solution: We shall apply the two conditions for static equilibrium on the ladder, 1 The sum of the forces acting on the rigid body is zero,!
Determine the forces and where they act on the ladder, remembering that the gravitational force acts at the center of mass of the ladder. You should draw a free body force diagram, clearly indicating the forces, and include unit vectors on the diagram. Identify any possible third law interaction pairs. Determine which point to calculate torque about. When calculating torque about a chosen point, you can always formally!
You may also argue geometrically if the given information of the problem makes it easier to compute the moment arm of the force about your chosen point or the perpendicular component of the force with respect to a line drawn from your chosen point to the point where the force acts. You still need to determine the direction of the torque.
Forces: Consider the forces acting on the person. The gravitational force acts at the center of mass of the person and the force on the person due to the contact between the person and!
The force diagram on the person is shown below. The normal force N pl that the person exerts on the ladder is part of a third law interaction pair. Denote the magnitude of N pl by N pl. Equation 3. The person exerts a downward contact force! The gravitational force between the earth and the ladder! At the point where the ladder is in contact with the wall, the contact force of the wall with! At the point where the ladder is contact with the floor, the contact force has! The force diagram is shown in the figure below Key point: The magnitude of the static friction force depends on the other forces and!
As the person walks up the ladder, the normal force of the person N pl changes position and hence the friction force will change in magnitude possibly causing the ladder to slip. The equations for static equilibrium of forces on the ladder using Equation 3. What external torque must be applied to the cylinder to keep it rolling? Problem 4 Solution: A choice of coordinate system is essential. There are many ways to do this problem, and several ways to select a coordinate system.
The solution presented here refers to vertical and horizontal forces. Any way the problem is done, it must be recognized that there are! Each contact force has two!
In an! There are many ways to solve such pairs of equations; the first method presented here is perhaps pedestrian, but it works. Multiply 4. Note that the moment of inertia of the cylinder, that is, whether the cylinder is hollow, solid, or something in between, does not enter the solution of this problem.
Alternate Solution: Not really an alternate solution, but different algebra. Re-express the second expressions in each of 4. Multiply the first equation in 4. Similarly, in the first expressions in Equations 4. Problem 5: Static Equilibrium Arm You are holding a ball of mass m2 in your hand. In this problem you will solve for the! Assume the outstretched arm has a mass of m1 , the center of mass of the outstretched arm is a distance s from the elbow, the tendon attaches to the bone a!
The force exerted by the person is equal to the weight of the person. Pulleys are used to lift heavy objects. The tension in the rope transfers our force applied in the downward or horizontal direction to lift the object in the upward direction.
Let us now at an example of the cables involved in the movement of an elevator. The value of tension in the cables is different in different states of motion. This is due to the fact that it depends on whether the elevator is moving against gravity or moving in the direction of gravity. The value of the maximum tension of the cable limits the weight that it can carry.
That is why the number of persons allowed in an elevator is limited. Tension is always positive. If the value of tension is negative then that means that the string is under compression. The value will be positive for any force that pulls the rope.
And, the value will be negative for any compressive force. Home Animation Quiz. Sign in. Forgot your password? Get help. Privacy Policy. Password recovery. Home Physics Tension force-Definition examples formula. Sled dogs pulling a sled using the tension in the cables. Share this: Twitter Facebook. Recent Posts. Fluid is a substance that does not have a definite shape and yields easily to external pressure.
It continually flows or deforms when it Michael addition reaction admin - January 7, 0. Michael addition was discovered by Arthur Michael in Michael's addition reaction is one of the most useful methods for the mild formation of The properties of any matter depend on the atomic configuration.
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