PHYS22_FC_02_Presentation PDF - Physics Notes

31. CCC Scale, Proportion, and Quantity Scale diagrams should show that noncontact (gravitational) forces are most relevant at the scale of the solar system and its bodies, then contact (electromagnetic) forces are more relevant at the scale of objects interacting on or within Earth, and th...

31. CCC Scale, Proportion, and Quantity Scale diagrams should show that noncontact (gravitational) forces are most relevant at the scale of the solar system and its bodies, then contact (electromagnetic) forces are more relevant at the scale of objects interacting on or within Earth, and then at the atomic scale the relevance shifts to noncontact (nuclear) forces 32. SEP Analyze and Interpret Data The momentum graph should be a straight line indicating steadily increasing momentum as the apple falls over time. Velocity increases by a rate of 9.8 m/s2 as the apple falls. Because neither the acceleration nor the mass change, the net force does not change. This supports Newton’s second law of motion. 33. SEP Construct an Explanation The third-law pair is Earth and the mass. Both exert the same magnitude of force on each other, but in opposite directions. Weight is exerted on the center of the mass.  34. SEP Plan an Investigation The mass is the independent variable, and the displacement of the spring when a given mass is attached is the dependent variable. The force exerted by the spring on each mass can be calculated by using the equation for weight, because the magnitude of the spring’s force will be equal to the magnitude of the weight of the mass. Hooke’s law can then be used to calculate the spring constant. 35. 250 N/m 36. 1.5 m  37. SEP Interpret Data The electric forces in copper must be comparatively weaker than the electric forces in steel. Types of Forces Objectives Analyze data to describe the mathematical relationships between the net force on an object, the mass of the object, and its acceleration. Use Newton’s laws to predict the motion of macroscopic objects. Can you guess how many forces are acting on you as you sit at your desk? 1. Gravitational Force (Weight): This force pulls you downward towards the center of the Earth due to gravity. 2. Normal Force from the Chair: This upward force counters your weight and prevents you from sinking into the chair. 3. Normal Force from the Desk: If you're resting your arms on the desk, this force supports the weight of your arms. 4. Frictional Force: The friction between you and the chair prevents you from sliding off. It’s fascinating to realize how even simple actions involve multiple forces working together to keep us in balance! What’s even more intriguing is that all these forces are in equilibrium, meaning they cancel each other out, allowing you to stay comfortably seated. If you have any specific questions about these forces, feel free to ask! Contact and Noncontact Forces Contact force: the interaction between objects due to direct contact with each other Noncontact force: the interaction between two objects that are separated by some distance What contact forces are shown in the image? The orangutan’s hands attached to the rope. The orangutan’s hands moving along the rope. The spring forces acting between the atoms within the rope. What noncontact forces are shown in the image? Gravity pulling the orangutan down. The electric forces and nuclear forces inside the atoms of the rope and the orangutan. Contact Forces 1.Rubbing your hands together generates heat due to friction. 2.A car skidding to a stop due to the friction between the tires and the road. 3.A string holding up a hanging plant. 4.A guitar string vibrating to produce sound. 5.A book lying on a table is supported by the table. 6.Leaning against a wall 7.Pushing a door open. 8.Lifting a box from the floor. Noncontact Forces 1. An apple falling from a tree to the ground. 2. The moon orbiting the Earth due to gravity. 3. A charged balloon sticking to a wall. 4. Magnets attracting or repelling each other. 5. The strong force holding protons and neutrons together in an atomic nucleus. 6. The energy released in a nuclear reaction. 7. A roller coaster car looping through a vertical loop. 8. A satellite orbiting the Earth. Weight Weight: the downward force experienced by objects resulting from the gravitational attraction to Earth Gravitational force: a noncontact attractive interaction between two objects Center of mass: the point representing the mean position of an object’s matter FEM = W = mg Weight How would our weight on a scale change if the mass of Earth suddenly changed? If Earth’s mass were to increase, the gravitational attraction would be greater so the weight shown on the scale would be greater. If Earth’s mass were to decrease, the gravitational attraction would be less so the weight shown on the scale would be less. Weight W is the force exerted by Earth on a mass and is measured in newtons, m is the mass in kg, g is the acceleration due to gravity and is –9.8 m/s2 on Earth. g on Earth is –9.8 m/s2. g on the moon is –1.6 m/s2. How much would a mass of 100 kilograms weigh on Earth and the moon? A 100-kg object would weigh 980 N on Earth and 160 N on the moon. Spring Force A deformation occurs in an object due to the application of a force. Spring constant: the spring’s resistance to deformation Hooke’s law: the size of a spring’s deformation is proportional to the applied force FSO = –kΔL Spring Force Would a spring with the higher or lower spring constant be easier to pull and compress? A spring with the lower spring constant would be easier to pull and compress.) Spring Force Why do you think there is a negative sign in front of the spring constant in the Hooke’s law equation? The negative sign is there because when you let go of the spring, it wants to go back to its original shape, which is the opposite direction from the applied force. Tension Tension is a contact interaction and is the pulling force on a rope, cable, or chain exerted along its length. The electric force is a noncontact interaction between two objects having electrical charge. Tension Surface Forces Surface forces: the spring-like interaction between two surfaces in contact with each other Friction: the parallel component of the surface force Static friction: the friction for attempted motion between two surfaces Kinetic friction: the friction for surfaces moving relative to each other Coefficient of friction: the amount of resistance between the two surfaces Modeling Force in Two Dimensions FFB N T fk W Centripetal Force Centripetal force: any force that causes an object to move in a circular path and is directed toward the center of the circular path Centripetal Force Why is it often said that the moon is “falling toward Earth” even though its average distance isn’t changing and it’s average speed isn’t changing? Centripetal Force The acceleration caused by Earth’s gravitational pull is causing the direction of the velocity to change because without it, the moon would continue to travel in a straight line, so the moon is constantly being pulled back toward Earth.