Properties of Matter Objectives Elasticity Hookes Law Density
Properties of Matter Objectives: • Elasticity, Hooke’s Law • Density and Volume, Specific Gravity • Pressure
Elasticity stress = applied force (N) Area (m 2)
Elasticity stress = applied force (N) Area (m 2)
Elasticity stress = applied force (N) Area (m 2) Applied Force (N) Stretching (m)
Elasticity stress = applied force (N) Area (m 2) Applied Force (N) Stretching (m) F 1. 0 cm 2 x. F ? cm 3 x. F ? cm 0. 5 x. F ? cm
Hooke’s Law for Springs
Hooke’s Law for Springs Hookes’ Law: applied force = (spring stiffness) (stretching)
Hooke’s Law for Springs Hookes’ Law: applied force = (spring stiffness) (stretching) Units: Lb -> (Lb/in) (in) N -> (N/m) (m)
Hooke’s Law for Springs Hookes’ Law: applied force = (spring stiffness) (stretching) Units: Lb -> (Lb/in) (in) N -> (N/m) (m) Q 1. A force of 3. 00 lb stretches a spring 12. 0 in. What force is required to stretch the spring 15. 0 in?
Elasticity 20 P 1. You apply a force on a solid rod. If you double the force applied, what happens to the stress? Ans. P 2. You apply a force on a solid rod. If you double the area over which the force is applied, what happens to the stress? Ans. P 3. A spring has a stiffness of 15 lb/in. If you apply 30 lb force on it, by how much does it stretch? Ans. P 4. You hang 50 g on a spring, and it stretches by 6. 0 cm. How much is its stiffness? Ans.
Density density Mass = Units: volume kg/m 3 lb/ft 3 Q 2. Which one has larger density? (a) A cup of fresh water. (b) A lake of fresh water (c) They are the same How do we find volume of an object? Cube: V = (side)3 Rectangular Block: V = (width) (length) (height) Sphere: V = (side)3 g/cm 3
Specific Gravity density = Mass volume Specific gravity = Density (material) Density (water)
Specific Gravity density = Mass volume Specific gravity = Density (material) Density (water) =1 water >1 Sinks in water <1 Floats in water Q 3. Kerosene has a specific gravity of 0. 82. Does it float or sink in water? (a) floats (b) sinks (c) I don’t know
Density 20 P 1. You have an object with volume of 1. 0 in 3 and mass of 316. 27 g. What is the most likely material it is made of? Ans. P 2. You have a cube with side 0. 5 in that is made of iron (7. 8 g/cm 3). How much is its mass? Ans. P 3. You submerge a block in water and find out that it displaces about 7. 5 m. L of water. You measure its mass as 58. 5 g. What is its density? Ans. P 4. Mercury is liquid at room temperature. Its specific gravity is 13. 6. Will it float or sink in water? Ans. P 5. A completely submerged object displaces its own (a) Volume of fluid (b) Weight of fluid (c) Density of fluid
Pressure = Force Area Units: N/m 2 = Pa Lb/ft 2
Pressure = Force Units: Area Q 4. How do you walk in snow without sinking? N/m 2 = Pa Lb/ft 2
Pressure = Force Units: Area N/m 2 = Pa Lb/ft 2 Q 4. How do you walk in snow without sinking? Half the Pressure Double Area Q 5. The earth’s atmosphere exerts about 100, 000 Pa on everything on the surface. If your effective area is about 0. 5 m 2, determine the force with which air “pushes you down”. 100, 000 = Force 0. 5 Force = 50, 000 N Mass = 5, 100 kg (11, 200 lb)
Pressure = Force Units: Area N/m 2 = Pa Lb/ft 2 Q 4. How do you walk in snow without sinking? Half the Pressure Double Area Q 5. The earth’s atmosphere exerts about 100, 000 Pa on everything on the surface. If your effective area is about 0. 5 m 2, determine the force with which air “pushes you down”. 100, 000 = Force 0. 5 Force = 50, 000 N Mass = 5, 100 kg (11, 200 lb)
Pressure = Force Units: Area N/m 2 = Pa Lb/ft 2 Q 4. How do you walk in snow without sinking? Double Area Half the Pressure Q 5. The earth’s atmosphere exerts about 100, 000 Pa on everything on the surface. If your effective area is about 0. 5 m 2, determine the force with which air “pushes you down”. Q 6. When you stand on one foot instead of two, the pressure you exert on the floor is: (a) less (b) more (c) the same
Pressure 20 P 1. When you stand on one foot instead of two, the pressure you exert on the floor is: (a) less (b) more (c) the same P 2. When you stand on one foot instead of two on a scale, the reading is (a) half (b) double (c) the same P 3. You apply 10 N force over 2. 0 m 2 area. What is the pressure in Pa? Ans.
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