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Describing Force and Motion ***Copy everything on slides 1-7 and then watch the rest of the slides.*** 1. What is FORCE and how is it measured? • A push or pull applied to an object • Measured in Newtons (N) • Measured with a spring scale 2. How are forces described? 10N 10N Net force = 0 no motion 20N 10N Net force = 10N to the right 20N 10N Same direction so … net force = 30 N to the right *net force – combination of all forces acting on an object • Balanced forces – all forces acting on an object are equal – There is NO MOTION • Unbalanced forces – one or more forces acting on an object are stronger than others – There is MOTION 3. What are SPEED and VELOCITY and how are they calculated? *Speed is the distance an object travels in a unit of time. 50 km/hr *Velocity is SPEED in a DIRECTION. 50 km/hr west • Sp = d/t • V = d/t include direction 4. What is MOTION? • Occurs when an object changes position relative to a reference point 5. What is Newton’s First Law? (Law of Inertia) Will stay at rest until force acts upon it. – An object at rest stays at rest and an object in motion stays in motion unless acted on by an unbalanced force – Inertia – tendency of an object to resist any change in its motion Gravity Will continue Friction in motion until these forces or the wall stops it 6. What is Newton’s Second Law? • Net force acting on an object causes the object to accelerate in the direction of the force. Force = mass X acceleration F = m x a or a = f/m or m = f/a 7. What is Newton’s Third Law? • For every action, there is an equal and opposite reaction. REACTION ACTION The truck is in motion. What is the force that causes it to stop? The push of the stopped car. The car is at rest. What is the force that causes it to move? The push of the truck. What about the ladder on top of the truck? The ladder is in motion because the truck is in motion. When the truck stops, the ladder stays in motion. The truck is stopped by the force of the car, but the ladder is not. What force stops the ladder? Gravity. The truck is in motion, the car is at rest. How do each of these vehicles accelerate? The truck stops moving. The car starts moving. Which one will be the hardest to accelerate? The truck because it has the most mass. Why does the car move [accelerate] when it is hit by the truck? The heavy and moving truck has more force than the small, at rest car. Why does the truck stop moving when it hits the car? The force of the car pushing back on the truck, plus the force of friction between the massive truck and the road slow down, the stop the truck. The truck hits the car. An action force stops the truck. What is the equal and opposite reaction force? The force that pushes the car forward.