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Mass and Acceleration. f. N. T. M. W. Types of Forces. Noncontact Forces. Contact Forces. Gravitational. Electromagnetic. Nuclear. Pushes. Pulls. Tension. Friction. Normal. Electric. Magnetic. perpendicular to surface. Newton’s 1 st Law:. No net force - no acceleration
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f N T M W Types of Forces Noncontact Forces Contact Forces Gravitational Electromagnetic Nuclear Pushes Pulls Tension Friction Normal Electric Magnetic perpendicular to surface
Newton’s 1st Law: • No net force - no acceleration • No acceleration = constant velocity
Dry Ice on Slate Motion of the Block Velocity Acceleration Push or Pull Necessary to Maintain Motion 0 0 0 at rest uniform motion to the right 0 0 moves to the right and speeds up without changing direction moves to the right, slows down and stops without changing direction
Fby snow Fby gravity Pretest #3(“the crate in the snow”) ?
Fby snow Fby gravity Pretest #3(“the crate in the snow”)
Nr,b Fnet a a Nr,b WE,b WE,b Newton’s 2nd Law: • Net force causes acceleration (not velocity) • The net force is the vector sum of all the individual forces on an object. Acceleration is in same direction as the net force.
f N T M W Which one is the net force? Types of Forces Noncontact Forces Contact Forces Gravitational Electromagnetic Nuclear Pushes Pulls Tension Friction Normal Electric Magnetic
What’s the mass? • A measure of “how much stuff” • A measure of how hard it is to speed up or slow down • Very different than weight!
F a Fnet a F a More net force - more acceleration(constant mass)
F 1 M a a F a More mass - less acceleration(constant net force)
M Fnet Fnet Fnet Constant × a a a M M Putting it all together Newton is defined such that constant = 1.
Scale reading = ? 10 N 1.0 kg
Scale reading = ? 10 N 20 N 2.0 kg
Free body diagram of 1 kg crate: TS,C (Reading on the scale) WE,C
In General • The force that the Earth exerts on an object of mass m is given byW = m (10 N/kg)
WE,J W = m (10 N/kg) Question: = m g • If Jeff jumps off the physics building in a vacuum, what will his acceleration be? (use Newton’s 2nd law) Fnet = m a WE,J = m a m (10 N/kg)= m a 10 N/kg is just g Weight force is given by mg
a = 4 m/s/s a = 4 m/s/s Nfloor,B T = 100 N M = 5 kg ffloor,B In the x-direction: Trope,B = 100 N Block Fnet = m a T - f = m a WE,B 2nd Law is the translator How big is the friction force? = 50 N = 80 N 100 N - f = (5 kg) (4 m/s/s) = m g = 50 N f = 80 N