* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Newton`s Second Law
Survey
Document related concepts
Center of mass wikipedia , lookup
Classical mechanics wikipedia , lookup
Jerk (physics) wikipedia , lookup
Coriolis force wikipedia , lookup
Equations of motion wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Seismometer wikipedia , lookup
Newton's theorem of revolving orbits wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Fictitious force wikipedia , lookup
Fundamental interaction wikipedia , lookup
Centrifugal force wikipedia , lookup
Classical central-force problem wikipedia , lookup
Newton's laws of motion wikipedia , lookup
Transcript
Chapter 3: Forces The amount of force needed to change an object’s motion depends upon the object’s mass and the acceleration used during the change. Newton’s Second Law F = force, units are Newtons (N) m = mass, units MUST be kg a = acceleration, units MUST be m/s2 Examples: 1. How much force is needed to accelerate a 1000 kg truck at a rate of 3 m/s2 ? F = ma F = (1000 kg)(3 m/s2) F = 3000 N 2. A force of 10 N is used to push a 10 kg box. What is its acceleration? F = ma 10 N = (10 kg)a a = 1 m/s2 3. Applying a force of 10 N to an object causes the object to accelerate at a rate of 5 m/s2. What is the mass of the object? F = ma 10 N = m(5 m/s2) m = 2 kg Types of forces Friction: a force that occurs when two touching objects move past each other. Frictional force is always in the opposite direction to the motion. Fapp Ff Ff Fapp Force More force Fapp Microwelds form where bumps come into contact. If the applied force is not big enough to break the microwelds, the object will not move. More downward force (weight) pushes the bumps closer together. This causes the static friction to increase. Types of forces Gravitational: occurs between any two objects and depends only the masses of the objects and the distance between them Fg F Fg g • The three Fg vectors show how the masses of the Earth, the moon and the astronaut attract each other. 1. Which one is the most significant to the astronaut? The vector between the astronaut and the Moon 2. To the Moon? The vector between the Moon and the Earth Force of gravity = weight Close to the Earth’s surface, all objects are accelerated by gravity at a rate of 9.8 m/s2 0s 5m 1s Fg 20 m 2s Fg = mg g = 9.8 m/s2 Projectile motion vy vy = 0 vx vx vx vy There is no acceleration in the x direction: vx is constant Gravity changes vy. In the first half of the throw, the upward motion of the ball is slowed down by gravity. In the second half of the throw, gravity accelerates the ball’s vy.