Motion Review What kinds of forces cause an object to change its motion? Unbalanced forces What might happen if an unbalanced force acts on a moving car? It would slow down/stop/crash What effect does balanced forces have on motion? NO MOTION What is speed? Distance per time What is velocity? Speed and direction What is acceleration? Change in velocity Either change in speed or direction, or both! What is the law of conservation of momentum? Momentum before a collision equals the momentum after a collision How does Newton’s Cradle represent conservation of momentum? The same number of objects that collide on one side move on the other Draw all of the forces acting on you as you sit still in your chair. Draw the action reaction pairs for: A larger student and smaller student sit on skateboard. The larger student pushes on the hands of the smaller student. If a student it sitting on a skateboard with a heavy medicine ball, then he throws the medicine ball in front of him. Which direction will he move? Backward Which law explains why the student in the previous example would move backwards? Newton’s 3rd: Action-Reaction I have penny inside a balloon. If I get the penny to spin around at a constant velocity, is it accelerating? Explain. Yes because it is constantly changing direction What is another name for Newton’s 1st law? Law of inertia What does Newton’s 1st law state? An object in motion stays in motion and an object at rest stays at rest unless acted upon by an unbalanced force What affects the amount of inertia an object has? Mass- More mass= more inertia What has more inertia- a bowling ball or a tennis ball? How do you know? Bowling ball b/c is has more mass What does that mean about changing the motion of the bowling ball versus the tennis ball? Because the bowling ball has more inertia, it will be more difficult to change its motion, so it will need more force (Newton’s 3rd) if you wanted to achieve the same acceleration. Explain why a skateboarder going down a hill would fall forward if he/she were to hit a rock. *The team that has the answer with the most vocabulary correctly used with win these points What does Newton’s 3rd law state? For every action there is an equal and opposite reaction Calculate how much force would be needed to accelerate a car that is 350 kg at a rate of 70 m/s/s. 24,500 N What F=ma is the formula for Newton’s 2nd law? Calculate the acceleration of snowboarder that comes to a stop in 6 seconds after traveling at a speed of 35 m/s. -5.83 m/s/s Calculate the acceleration of an object that has a mass of 76kg and is being pushed with a 120 N force. 1.5 m/s/s Calculate the velocity of a plane that is traveling from Maine to Florida if it travels 612 miles in 2 hours. 306 miles/hr If you are pushing a box across the floor, what happens to the acceleration of the box if a mass is added and you push with the same force? It decreases You are using a sling-shot to shoot a rock. After your first trial, you want to make it for farther. You cannot change the angle that you aim at. What change could you make to get the rock to travel farther? Pull the rubber band farther back because it increases the force. 2 students are sitting on skateboards (similar to our class demonstration). If the larger student pushes on the smaller student, why does the smaller student accelerate more than the larger student? Because he/she has less mass and according to Newton’s 3rd law the same amount of force was acting on both students and Newton’s 2nd law says that objects with less mass accelerate more with the same amount of force. What 2 possible changes can you make to increase an object’s acceleration? Increase the force or decrease the mass What is the relationship between mass and gravitational pull? More mass=greater gravitational pull Other than mass, what else affects the amount of gravitational pull? Distance Weight is a force. What should the unit of weight be? NEWTONS Just a reminder: MASS vs WEIGHT Mass is amount of matter in an object, weight is a measure of the effect of gravity on an object. Your MASS NEVER changes. Your weight can, depending on gravity! Use all of Newton’s Laws to explain the motion of a baseball that is being hit with a bat. Explain why a rocket can move through outer space where there is no matter for it to push on. According to Newton’s 1st law, an object in motion will stay in motion (same direction and same speed) unless an outside force acts upon it. It is already in motion, so it will continue to do so until there is an unbalanced force to act on it. A hovercraft, which moves over water on a cushion of air, can achieve greater speeds that ordinary boats. Explain why this is possible. The air reduces the amount of friction acting on the boat. Friction is one of the common unbalanced forces that causes a change in motion. With less friction, there is less of a force acting against motion. Use Newton’s 2nd law to explain why large trucks get fewer miles per gallon of gas than smaller cars. It takes a greater force to move the larger truck with the same acceleration as the smaller car because it has more mass. According to Newton’s 2nd law, it takes more force to accelerate an object with a greater mass.