Forces in One Dimension Vocabulary - Section 1 ▪ Force • Equilibrium ▪ Balanced forces • Newton’s first law ▪ Unbalanced forces • Newton’s second law ▪ Free body diagrams • Newton’s third law ▪ Net force • system ▪ Contact force ▪ Field force ▪ Inertia Force and motion ▪ In physics, a force is a push or pull ▪ Unbalanced forces change motion ▪ Objects at rest, or not moving, still have forces acting upon them. These are known as balanced forces ▪ Contact forces – forces that directly touch the object (ex. Your hand pushing an object or simply holding an object) ▪ Field forces – forces that are exerted without contact. (ex. Gravity) Force and Motion ▪ Free body diagrams – a pictorial representation of forces acting on an object – the object is depicted by a dot – Each force is represented by a vector (arrow) showing the direction of the force on the object – The length of the vector must be proportionate to the force acting on the object (use the magnitude of the vector) – Each force must be labeled. Ex. Draw a Free body diagram of a person holding a ball in their hand: Fhand on ball Fgravity Force and motion ▪ Forces are measured in Newtons ▪ 1 N = kgㆍm/s2 ▪ The force exerted by an apple on your hand is approximately 1 Newton. Force and Motion ▪ Net force – the vector sum of the forces acting on an object – To calculate net force: ▪ If forces are being applied in the same direction, then add forces together ▪ If forces are being applied in opposite directions, then subtract forces. Newton’s 2nd law ▪ Newton’s 2nd law states the force is directly proportional to the mass of an object and its acceleration. ▪ 퐹푛푒푡 = 푚푎 ▪ The equation can be arranged to find acceleration 퐹 ▪ 푎 = 푛푒푡 푚 Ex. Two people are fighting over a pillow with a mass of 0.30 kg. If one person pulls with a force of 10 N and the other person pulls with a force of 11 N, what is the horizontal acceleration of the pillow? Newton’s 1st law ▪ Newton’s 1st law states that an object at rest will stay at rest and an object in motion will continue to move in a straight line with a constant speed if and only if the net force acting on the object is zero. ▪ Newton’s 1st law is sometimes caused the law of inertia ▪ Inertia – (not a force) - an objects tendency to resist a change in velocity. Newton’s 1st law ▪ Equilibrium – the net force acting on an object is zero – An object is in equilibrium if it is moving at a constant velocity. – Being a rest, v= 0, is also equilibrium.