Scalars, vectors, displacement, velocity, acceleration, Newton's laws, momentum, pressure ยท 20 terms
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A quantity that has magnitude only, with no direction.
Like saying a bag weighs 5 kg โ just a size, no direction needed.
A quantity that has both magnitude and direction.
Like giving directions: 5 km north โ you need both the amount and where.
The quantity of matter in a body, regardless of its volume or any forces acting on it.
Mass is how much "stuff" is in something. It never changes no matter where you are โ on the moon or on Earth.
The force of gravity acting on a body.
Weight is the pull the Earth has on your mass. The same person weighs less on the Moon because gravity is weaker there.
Weight = mass ร gravitational field strength (W = mg). Weight is a force, not the same as mass!
The total path length travelled by an object.
If you walk around a square field and come back, distance = full perimeter walked.
The distance travelled in a given direction โ the straight-line distance from start to finish.
Driving 3 km north then 4 km east โ displacement is 5 km northeast (the straight line), but distance is 7 km.
Displacement is a vector. Always state the direction.
The distance travelled per unit time.
The rate of change of displacement with respect to time โ speed in a stated direction.
A car doing 60 km/h around a corner is at constant speed but changing velocity because direction is changing.
Velocity is a vector. Distinguish it clearly from speed in exams.
The rate of change of velocity with respect to time.
A car accelerating from 0 to 60 km/h in 10 s โ the change in velocity per second.
Can be negative (deceleration). a = (v-u)/t
Anything that causes a body to accelerate โ a push or pull that changes the state of rest or motion of an object.
A kick is a force โ it changes the motion of a football.
A body remains at rest or in uniform motion unless acted upon by an external resultant force.
A book on a table stays still because the forces balance. A puck on ice keeps sliding because there's almost no friction.
Key word: "resultant" force. If forces balance = no acceleration, not necessarily no motion.
The rate of change of momentum of a body is directly proportional to the applied force and takes place in the same direction as the force. (F = ma)
A heavier shopping trolley needs more force to accelerate at the same rate as an empty one.
F = ma. Also expressible as F = ฮp/ฮt. Both forms may be needed.
For every action there is an equal and opposite reaction.
When you push off a wall, the wall pushes you back equally. Rocket thrust: gases expelled down, rocket goes up.
Forces act on DIFFERENT objects. They don't cancel each other.
The product of a body's mass and velocity.
A slow-moving lorry can have more momentum than a fast bicycle because of its huge mass.
p = mv. Momentum is conserved in collisions if no external force acts.
In a closed system where no external forces act, the total momentum before a collision equals the total momentum after.
Two ice-skaters pushing off each other: both move apart, but total momentum stays zero.
Always check: is the system closed? State this in your answer.
The force that opposes relative motion between two surfaces in contact.
Rubbing your hands together โ that resistance is friction, which also generates heat.
The force of gravity acting on a body. W = mg.
Mass per unit volume.
Lead is dense โ lots of mass packed into a small space. Foam has low density โ lots of volume, little mass.
ฯ = m/V
Force per unit area.
A stiletto heel exerts far more pressure than a flat shoe โ same force, tiny area.
P = F/A. 1 Pa = 1 N/mยฒ
The amount of space that a substance or object occupies.