🔖 Topics

  • Gravitational Force
  • Friction Force

🎯 Objectives

  • Introduce friction into statics problems
  • Gain familiarity with the equation for gravitational force

📋 Sequence

  • Talk about due date of pre-lab quiz vs lab writeup
  • Answer questions about reading / homework
  • Go through practice problems for friction and gravitational force

🖥️ Animations, Simulations, Activities

N/A

📝 Practice Problems

Pulling a Suitcase: You are pulling a suitcase through the airport at a constant speed by exerting a force of 25.0 N at an angle of \(30^\circ\) from the vertical. What is the force of friction acting on the suitcase?

Field Strength Above the Earth: The gravitational field strength at the surface of the Earth is 9.8 \(m/s^2\).

  • How far above the Earth would the field strength be \(2/3\) the value at the surface?
  • How far above the Earth would the field strength be \(1/3\) the value at the surface?

Eclipses: Calculate the net gravitational force on the Moon from the Earth and Sun during a lunar eclipse (i.e. the Earth is between the Sun and the Moon). Do the same for a solar eclipse (i.e. the Moon is between the Earth and the Sun).

Binary Star System: A binary star system consists of two stars with masses \(M\) and \(4M\) that are a distance \(d\) apart.

  • Sketch a diagram of the system with arrows showing the direction of the gravitational field around the stars.
  • Where would the gravitational field be equal to zero around these stars?

Sliding Point: A box with mass \(M_{box}\) is sitting on a table with a coefficient of static friction \(\mu\). I slowly start to tilt the table upwards. At what angle \(\theta\) will the box start to slide?

Framed Picture on a Wall: While trying to decide where to hang a framed picture, you press it against the wall to keep it from falling. The picture weighs 5.0 N, and you press against the flat frame with a force of 6.0 N at an angle of \(40^\circ\) from the vertical.

  • What is the direction of the normal force exerted on the picture by your hand?
  • What is the direction of the normal force exerted on the picture by the wall?
  • What is the minimum coefficient of static friction between the wall and the picture?
  • Depending on the magnitude of the force you exert, the frictional force exerted on the picture by the wall could have either of two possible directions. Why?

✅ Partial Solutions

N/A

📘 Connected Resources

  • Giambattista, Alan, et al. College Physics With an Integrated Approach to Forces and Kinematics. 5th ed., McGraw-Hill Education, 2020.