Circular Motion

Physics D began their work with circular motion today with an overview of centripetal acceleration and centripetal force. We contrasted tangential and angular speed, then looked at how those different speeds were impacted by tangential and centripetal acceleration. Remember that tangential acceleration works on changing the speed of the motion and centripetal acceleration is involved with changing the direction. We then looked at centripetal acceleration and how many forces can do this job. Tomorrow, we take on the idea of gravity, a force can serve as a centripetal force. This is where Physics F picked up today. We looked at how Newton pulled together the pieces of the idea of gravity and the formula for Universal Gravitation. The homework tonight will allow you practice with this idea and tomorrow we'll jump over Kepler's Laws of Planetary Motion and take on the concept of torque.

Honors Physics concentrated on center of mass, moment of inertia and rotational equilibrium today. We defined center of mass and it paved our way for a discussion of moment of inertia - the resistance of an object to changes in rotation. We looked at how different shapes have different moments of inertia, with the general rule of thumb that the further an object's mass is away from the selected axis of rotation, the higher the moment of inertia and the harder it is for a torque to produce acceleration. We then looked at the two conditions of equilibrium and ended class at the point where we'd begin to look at problem solving, so that's where we'll pick up tomorrow.

Intro Physics took on the idea of the impulse-momentum theorem, using yesterday's lab to highlight our discussion. The impulse an object experiences (force x time) is equal to an object's change in momentum and we looked at how this principle applies to situations involving safety nets/airbags and follow-through in sports. For the same theoretical momentum change, the longer the duration of the situation, the smaller the force the object experiences and for a maximum momentum change, given a limited force, prolong the contact as much as possible. Tonight's homework gives you practice with the math of this concept and tomorrow we'll see how impulse and Newton's 3rd Law of Motion lead to a new concept - conservation of momentum.