College Physics I - PHYS 1301.001 - Homework 6

College Physics I - PHYS 1301.001

• Homework 6 is on Mastering Physics and due on Monday, March 10.
• The course is PHYS 1301.001 Spring 2025 section Khan50126
• Reviews and discussion sessions are with Dr. Khan.
• Review sessions are held in SCI 3.265 on Wednesdays from 11 am to 12 pm and Thursdays from 1 pm to 2 pm.

Physics Help

• Crosby Pineda can be reached at [email protected] and available Mondays 1 pm - 2 pm SCI 3.253, 2 pm- 3 pm SCI 3.265.
• Muhammad Khalid can be reached at [email protected] and available Tuesdays and Thursdays 12 pm - 1 pm, SCI 2.179.
• Meghraj Magadi Shivalingaiah can be reached at [email protected] and available Fridays 2 pm - 3 pm, SCI 2.112.
• Anusha Srivastava can be reached at [email protected] and available Mondays 2 pm - 3 pm, SCI B.139.
• Mahammed Patel can be reached at [email protected] and available Tuesdays 10.30 am to 11.30 am and 1.00 pm to pm, SCI 3.253.
• Rittik Patra can be reached at [email protected] and available Thursdays 2:30 pm-3:30 pm, SCI 2.112.
• Online Problem Sessions (OPS) are held on Teams on Fridays at 3 pm.

Supplementary Instruction

• Tahir Ali offers supplementary instruction Tuesdays and Thursdays from 4-5:15 in MC 3.606B.

Newton's Laws of Motion (Chapter 4)

• The chapter covers force, Newton's First, Second, and Third Laws, mass, weight, and free-body diagrams.

Force and Interactions

• Kinematics describe motion in one, two, or three dimensions.
• Dynamics relates motion to the forces that cause it.
• Newton's Laws of Motion clearly state the principles of dynamics.
• These laws were deduced from experiments.
• Force is an interaction between two bodies or between a body and its environment.
• Contact force involves contact between bodies.

Common Types of Forces

• Normal Force is exerted by a surface on a body in contact with it, acting perpendicular to the surface.
• Friction Force is exerted by a surface on a body, acting parallel to the surface.
• Tension Force is a pulling force exerted by a stretched rope or cord. It is a contact force.
• Long range forces include magnetic and gravitational forces.
• Weight is the gravitational force exerted by the earth on a body.

SI Unit of Force

• The SI unit is the newton (N).
• 1 N = 1 kg·m/s².
• Force is described by direction and magnitude.

Typical Force Magnitudes

• Weight of a large blue whale: 1.9 × 10^6 N
• Maximum pulling force of a locomotive: 8.9 × 10^5 N
• Weight of a 250-lb linebacker: 1.1 × 10^3 N
• Weight of a medium apple: 1 N
• Electric attraction between the proton and the electron in a hydrogen atom: 8.2 × 10^-8 N
• Gravitational attraction between the proton and the electron in a hydrogen atom: 3.6 × 10^-47 N

Measuring Force

• The spring balance measures force magnitudes.
• Vectors represent applied forces.
• The length of the vector indicates the force magnitude.

Superposition of Forces

• Several forces acting at a point on an object have the same effect as their vector sum.
• The vector sum of all forces on an object is the resultant or net force.

Decomposing Forces

• Choose perpendicular x- and y-axes to decompose forces.
• Fx and Fy are the components of a force along these axes.
• Use trigonometry to find the force components.

Newton's Laws of Motion

• 1st Law: A body acted on by no net force moves with constant velocity (which may be zero) and zero acceleration.
• 2nd Law: If a net external force acts on a body, the body accelerates in the direction of the net force; the mass of the body times the acceleration of the body equals the net force vector.
• 3rd Law: If body A exerts a force on body B (an "action"), then body B exerts a force on body A (a "reaction"). These two forces have the same magnitude but are opposite in direction and act on different bodies.

Newton's First Law - Inertia

• When a body is at rest or moving with constant velocity (in a straight line with constant speed), it is in equilibrium.
• Equilibrium requires no forces or forces that sum to zero.
• Net force causes acceleration.
• A hockey puck accelerates in the direction of the net applied force.
• When no net force, the acceleration is zero, and the puck is in equilibrium.
• Inertia is a body's tendency to maintain its state of motion.

Newton's Secons Law - Inertial Mass

• When a net force acts on a body, the body accelerates in the same direction as the net force.
• Inertial mass is the ratio of the magnitude of the net force to the magnitude of acceleration.
• Mass is a measure of inertia.
• The unit of mass is the kilogram (kg).

Newton's Second Law - Mass and Weight

• The weight of an object on Earth is the gravitational force exerted on it.
• The weight (w) of an object of mass (m) can be determined.
• The value of g depends on altitude and location.

Applying the Laws - Example

• Consider a worker pulling a 40 kg box with a 20 N horizontal force on a frictionless frozen lake.
• The vertical forces are in equilibrium, resulting in no vertical motion.
• There is a net force along the horizontal direction, and thus acceleration.

Free-Body Diagrams

• Newton's laws apply to a specific body.
• Only forces acting on the body matter.
• Free-body diagrams help identify relevant forces acting on the body.
• Do not include forces the body exerts on other bodies.
• Action-reaction pairs do not appear in the same free-body diagram.

Force and Motion Problem Strategy

• Analyze the problem with a pictorial representation.
• Analyze the motion with a motion diagram to determine the acceleration vector.
• Identify all forces on the object via a free-body diagram.
• Apply Newton's Second Law.
• Determine the vector sum of forces from the free-body diagram.
• Solve for the motion using kinematics.
• Evaluate the results.