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In these Physics Lecture Slides, following major aspects of physics have been discussed : Forces, Motion, Weight, Free Fall, Force, Motion, Normal Force, Tension, Terminal Velocity, Air Resistance
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Newton’s Laws of Motion
to stay in motion. An object at rest tends to stay at rest.‖
action there is an equal but opposite reaction.‖
in the same direction with the same speed until some net force acts on it.
unless a net force acts on it.
to change a body’s velocity.
“An object in motion tends to stay in motion; an object at rest tends to stay at rest.”
2
nd Law: F net = m a
For a while, we’ll only deal with forces that are horizontal or vertical.
When forces act in the same line, we can just add or subtract their magnitudes to find the net force.
2 kg
a
a
“For every action there’s an equal but opposite reaction.”
Earth / Apple How could the forces on the tennis ball, apple, and bullet, be the same as on the racquet, Earth, and rifle? The 3rd^ Law says they must be, the effects are different because of the 2nd^ Law!
Earth
apple 3.92 N
0.40 kg
5.98 1024 kg
A 0.40 kg apple weighs 3.92 N ( W = mg ). The apple’s weight is Earth’s force on it. The apple pulls back just as hard. So, the same force acts on both bodies. Since their masses are different, so are their accelerations (2nd^ Law). The Earth’s mass is so big, it’s acceleration is negligible.Docsity.com
Suppose an International Space Station astronaut is on a spacewalk when her tether snaps. Drifting away from the safety of the station, what might she do to make it back?
Due to the 3rd^ Law, when you swim you push the water (blue), and it pushes you back just as hard (red) in the forward direction. The water around your body also produces a drag force (green) on you, pushing you in the backward direction. If the green and red cancel out, you don’t accelerate (2nd^ Law) and maintain a constant velocity.
Note: The blue vector is a force on the water, not the on swimmer! Only the green and red vectors act on the swimmer.Docsity.com
