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| 3.8: Forces and Structures (page 152-153) Pg. 8 2) Scalar quantities have a magnitude but not a direction, e.g., temperature. Vector quantities have both magnitude and a direction, e.g., force. 3) Force is a push or a pull acting upon an object as a result of its interaction with another object. 4) The force is measured in Newton (N) which is defined as the force which causes an object with a mass of 1 kg to accelerate at a rate of 1 m/sec each sec. 5) Torque is the force about the point of rotation of an object. It is calculated by multiplying the magnitude of the applied force and the rotation pivot of the object. 6) Examples of force are gravity, attraction, electrical force, magnetic forcr, friction, spring force, tensional force, resistance, and etc. 7) Magnitude is a measure of how strong the force is. 3.8: Forces and Structures (page 152-153) Pg. 13 Practice: 1. Find the force of an object with a mass of 10 kg and acceleration of 2 m/s2. F = m x a = 10 kg x 2 m/s2 = 20 kg. m/s2 = 20 N 2. Christina travelled a total distance of 200 m. Her trip took 5 sec. Find the acceleration. v = d = 200 m = 40 m/s t 5 sec a = v = 40 m/s = 8 m/s2 t 5 s 3. What is the weight of a 4 kg rock? W = m x g = 4 kg x 10 N/m2 = 40 N 4. Find the torque acting on an object if the applied force is 50 N and the moment arm is 10 m. T = F x r = 50 N x 10 m = 500 N.m or 500 kg. m2/s2 3.10: Loads (page 156 - 157) Pg. 5 1. Hydro towers form a structure that is used to carry electricity from generating �(see question # 1 and figure 4 page 157) The dead load is the tower itself, the live load is the wires. The dynamic load is the forces of nature, such as wind, rain, ice, etc. 3. Shopping bags have a low dead load. Would a shopping bag with a high dead load still serve its purpose? Explain. A shopping bag witha a high dead load might be stronger because it would probably be made from stronger materials (most clothe bags have a higher dead load than plastic). However, if the dead load were too large, the bag might be too heavy for people to carry! 4. Load is the effect of the forces acting on a structure. It is grouped into two categories: A) static loads & B) dynamic loads A) Static Load is the load caused by gravity. It is divided into two loads: 1) Dead Load which is the static load caused by gravity acting on the mass of a structure; the weight of the structure. It does not change. 2) Live Load which is the static load caused by gravity acting on all of the things in and on a structure that are not part of the structure. It can vary. B) Dynamic Load is the load on a structure caused by a force other than gravity (riding a bicycle, pushing a chair, etc.) 3.12: Tension, Compression, Torsion, and Shear (page 160-161) Pg. 6 4) In your own words, describe tension, compression, torsion, and shear. Tension: a pulling force Compression: a pushing-together force Torsion: a twisting force Shear: a force that uses two parallel, opposite forces BLM 3.12.1: Tension, Compression, Torsion, and Shear. See (page 160-161) for the correct answers. |