Forces in One Dimension

Vocabulary - Section 1 Equilibrium Newton’s first law Newton’s second law Newton’s third law system Force Balanced forces Unbalanced forces Free body diagrams Net force 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. 𝐹 𝑛𝑒𝑡 = 𝑚𝑎 The equation can be arranged to find acceleration 𝑎= 𝐹 𝑛𝑒𝑡 𝑚 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