By the end of Week 3, you should: · Understand what translational equilibrium of an object (a "particle") is · Be able to set up (and solve) three equations of translational equilibrium · Know the types of forces we will be dealing with · Understand which forces are internal, and which are external · Understand the principles behind drawing free-body diagrams (including which forces to include, and which forces to not include), and be able to draw them . Understand how to deal with a force whose direction is not known · Solve 2D and 3D problems about translational equilibrium of an object . Understand scalar and vector definitions of the moment of a force . Be able to find the resultant moment of a system of forces in 2D using the scalar definition of the moment of a force · Know and be able to use the right-hand rule(s) · Understand the reason(s) behind describing rotation with the help of a vector · Know what a cross-product of two vectors is · Know how the magnitude of the cross-product of two vectors is related to their magnitudes and the angle between them, and how the direction of the cross-product can be determined · Be fluent with mutual cross-products of the ort vectors ( i, j, k ) . Be able to calculate the cross-product of two vectors by setting up a determinant containing the ort vectors and the Cartesian components of the two vectors in question · Understand how cross-product can be useful for determining the moment of a force . Understand how scalar and vector definitions of the moment are connected Questions · Why at all do we care about drawing free-body diagrams? . Why do we not include the internal forces (the forces acting between different parts of the object) into its free-body diagram? Can you name a law of physics that substantiates this? . What is the physical meaning, in words, of the equations: EFx = 0, EFy = 0, EF2 = 0? . So why did we introduce the vector definition of a moment? Why didn't we want to stick to its scalar definition only? . Give the scalar and the vector definitions of the moment of a force in full sentences, carefully defining all the physical parameters (aka "letters in the equations") that you need to introduce. . In which type(s) of problems the scalar definition of the moment is more convenient than its vector definition? Conversely, in which type(s) of problems the vector definition of the moment is more convenient than its scalar definition? · Assume that a rotation is described by a moment: a) M = 57; b) M = - 3k; c) M = 27 + 2]. Can you describe these rotations in words? . Can you explain why the scalar and the vector definitions of the moment of a force define one and the same physical quantity?