Net Force Particle Model

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# Net Force Particle Model - PowerPoint PPT Presentation

Net Force Particle Model. Newton’s Law Problems- unbalanced forces. Key Ideas . The amount by which the forces acting on an object are unbalanced is called the net force. When forces acting on an object are unbalanced, the object will accelerate.

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## Net Force Particle Model

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### Net Force Particle Model

Newton’s Law Problems- unbalanced forces

Key Ideas
• The amount by which the forces acting on an object are unbalanced is called the net force.
• When forces acting on an object are unbalanced, the object will accelerate.
• Acceleration is a change in velocity, and velocity includes both magnitude (speed) and direction, so a net force will change the speed and/or the direction of an object’s motion.
• Forces may be balanced in one direction and unbalanced in the other.
Newton’s 2nd Law
• The net force on an object divided by its mass equals its acceleration
• (Fnet) / m = a
• Fnet = ma
• Use Newton’s 2nd Law to qualitatively describe the relationship between: mass and acceleration, force and acceleration and mass and force.
• If you double the mass, the acceleration will change by a factor of ….?
• Use Newton’s 2nd Law to solve quantitative problems involving F, m and a.
• Use a force diagram to find the net (unbalanced) amount of force.
• List force and motion variables – knowns and unknowns. (next slide)
Newton’s 2nd Law
• List force and motion variables – knowns and unknowns.
• Force Equation: Fnet = maForce Variables: acceleration, mass, net force
• Motion Equations (Kinematic Eqns):Motion Variables: acceleration, initial velocity, final velocity, ∆t, ∆x (displacement)
• Common variable: acceleration
• Use what you know to solve for acceleration, then use it to solve for unknowns.
Sample Problems
• Draw a force diagram for a 900-kg car that exerts 5000-N of traction force on a level road while being opposed by 1000-N of friction and drag forces combined.
• Write the net force equation for the car.
• Calculate the acceleration of the car.
• Draw a force diagram for a block sliding to a stop.
• Label the magnitude of the forces for a 5-kg block that is initially traveling at 30 m/s and slows to a stop in 5 sec.