energy and force Flashcards
what’s the difference between speed and velocity?
speed is a scalar quantity meaning it is just a number but velocity is a vector meaning its a number and direction.
how do you work out speed form a distance time graph?
find the gradient. The steeper the gradient, the higher the speed
what is newtons third law?
When two objects interact, the forces they exert on each other are both equal and opporsite.
what is terminal velocity?
Where a frictional force increases with speed up to a certain point.
how do you reach maximum terminal velocity?
As the speed of the object increases,the resitance therefore increases. This gradually reduces the acceleration until the resistance force is equal to the acelerating force. When this happens it will stop accelerating, as the forces are balanced.
how do you calculate acceleration from a velocity time graph?
the gradient
how do you calculate displacement (distance travelled) from a velocity time graph?
area under the curve
mass definition
measure of how much ‘stuff’ (matter) an object is made up of.
weight definition
the force of gravity on an object. Since weight is a measure of force, its standard unit is the newton (N). You measure it with a spring balance, or a newton meter.
gravity definition
the force that attracts objects towards the centre of the earth (ie: the ground), or towards any other physical body having mass.
what is newtons first law?
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
what is newtons second law?
The resultant force on an object (measured in Newtons) is equal to the mass of the object (measured in kg) multiplied by the acceleration (measured in N/kg or ms-2 - the units are equivalent).
what are the three types of friction?
Sliding friction: when solid objects or surfaces are rubbing together.
· Static friction: when two solid surfaces are gripping each other.
· Drag or air resistance: this is friction from liquids or gases.
braking distance is influenced by what factors?
-Mass of the car
-How good the brakes are
-How fast you’re going
-Friction
what does air resistance (type of friction) depend on?
-speed
-surface area of object
what is power?
the rate of energy transfer
what is the conservation of energy law?
Energy can neither be created nor destroyed. It can only be transferred from one form to another.
what is potential energy?
the energy stored in an object due to its position.
what is gravitational potential energy?
the amount of potential energy the object has due to its position above the ground.
what is kinetic energy?
the amount of energy a moving object has, and is dependent on its mass and its speed.
maximum kinetic energy =
maximum gravitational potential energy
what is momentum?
“mass in motion”. All objects have mass, and when they move, they have momentum
what is the conservation of momentum?
When objects collide, and as long as no external forces are acting on them, their momentum is conserved, ie: the total momentum after the collision is the same as the total momentum before the collision. We can use this idea to work out the mass, velocity or momentum of an object in an explosion or collision.
what is a spring constant?
measures the stiffness of an elastic object up to its limit of proportionality.
what is the limit of proportionality?
(also known as the elastic limit) is the point of extension when Hooke’s law is no longer true- beyond this, the material or object will no longer return to its original shape after stretching (this is called inelastic deformation).
what is a magnet?
an object that exerts a force on another nearby magnet. Magnets have a North pole (the end that is attracted to the Earth’s North pole), and a South pole (the end that is attracted to the Earth’s South pole). Magnetic forces are non-contact forces, so occur without the objects touching.
two objects can attract or repel according to what rules?
-If the poles are the same, then the magnets repel each other, e.g. North to North or South to South
-If the poles are opposite to each other, then the magnets attract each other, e.g. North attracts South, and South attracts North
what are the key features of a magnetic field?
-the arrows show the direction of the magnetic force, from N -> S
-the lines never touch each other
-the magnetic field increases in strength when the lines get closer together
In an electromagnet what is the relationship between current and the magnetic field?
the stringer the current, the stronger the magnetic field
what is a solenoid?
a coiled wire and produces a magnetic field. The magnetic field inside the solenoid is pretty strong and importantly, consistent. Now, take that solenoid and put an iron core in it. The iron core strengthens the magnetic field, giving you an electromagnet.
what is the motor effect?
when a wire carrying a current interacts with a magnetic field, causing it to move at a right angle. when a wire carrying a current interacts with a magnetic field, causing it to move at a right angle.
how do you work out the direction of force on the wire?
using flemings left hand.
-thuMb = Movement
-First finger = Field (North to South)
-SeCond finger = Current (Positive to Negative)
So, align your first finger with the direction of the magnetic field, and your second finger with the current. Then, look at the direction your thumb is pointing in. That’s the direction the wire will move in.
