P4- Explaining Motion Flashcards
Distance time graph?
- Gradient= speed
- Flat sections= stationary
- Steeper slope= faster it’s going
- “downhill” sections means it’s coming back to starting point
- Curves- acceleration and deceleration
- Steeper curves- faster
- Levelling off curves- decelerating
Displacement graphs?
- The gradient tells you the velocity.
- Can be positive or negative
- Everything else is the same as distance time graphs.
What is velocity?
- Describes speed and direction.
- Instantaneous velocity is the speed and direction at a given moment in time.
- You can have negative velocities.
What is acceleration?
Acceleration is the change in velocity (or speed) in a certain amount of time.
Acceleration formula?
Acceleration (m/s squared) = change in velocity (m/s) / time taken (s)
Velocity time graphs?
- Gradient = acceleration
- Flat sections = constant speed
- Steeper gradient = greater acceleration/deceleration
- Uphill section (/) are acceleration
- Downhill sections () are deceleration
- A curve means changing acceleration
- Negative velocity means the object is travelling in the opposite direction.
What is gravitational potential energy?
It is energy stored in an object when you raise it to a height against the force of gravity.
Equation for GPE?
Change in gravitational potential energy (J) = Weight (N) * Vertical height difference (m)
Conversion of GPE to KE?
When something falls its gravitational potential energy (GPE) converts to kinetic energy (KE).
Equation for GPE to KE?
KE gained = GPE lost
What is kinetic energy?
Anything that’s moving has kinetic energy. The kinetic energy of something depends on its mass and speed.
Equation for kinetic energy?
Kinetic energy (J) = mass (kg) * velocity squared. (m/s squared)
How do you increases something’s KE?
To increase something’s kinetic energy you need to increase its velocity.
To increase the velocity you apply force to it.
What does it mean when energy is conserved?
This means you can’t create or destroy energy. It gets transformed into one kind of energy to another.
Why is energy lost while work is done?
The increase in an object KE is normally a bit less than the amount of work done on it, because some energy is wasted as heat.
What does “work done” mean?
When a force moves on an object it does work and energy is transferred to the object.
Work done equation?
Amount of energy transferred (j) = work done (j)
Work done by a force equation?
Work done by a force (J) = force (N) * distance moved in direction of force (m)
Change of momentum equation?
Change of momentum (kg m/s) = resultant force (N) * Time for which the force acts (s)
Car safety features?
- Crumple zones- crumple on impact- increases the time taken for the car to stop.
- Air bags- Slows you down gradually.
- Seat belts- increases the time taken for the wearer to stop. This reduces the forces acting on the chest.
- Cycle and motorcycle helmets- provides padding that increases the time taken for your head to come to a stop if it hits something hard.
Arrows representing forces?
- The length of the arrow shows the size of the force.
- The direction of the arrow shows the direction of the force.
- When arrows are opposite but are all the same size. The forces are balanced.
What is the resultant force?
It is the overall force acting on the object. You can get this amount by adding the individual forces.
What are an interaction pair of forces?
When an object exerts a force it always experiences a force in return. This is called interaction pair of forces.
What is a reaction force?
It is a force which is a “response” to an object which exerts a force on it.
For example, if you put a book on a table, the book pushes on the table with a force equal to its weight.
And the table exerts an equal and opposite force upwards on the book. That is called the reaction force.
What is friction?
When an object is moving relative to another one, both objects experience a force in the direction that opposes the movement - this is friction.
Is friction a reaction force?
• Friction is a reaction force- it happens as a result of an applied force.
Friction between solid surfaces which are gripping?
This type of friction is gripping.
It lets you walk the friction between your shoes and the ground allows you to push against it and move forwards.
Friction between solid surfaces which are slipping??
Two objects slide past each other.
You can reduce sliding friction and gripping friction by adding a lubricant like grease or oil between the surfaces.
What is drag?
Drag is a type of friction.
An object moving through a fluid has to force its way past the molecules in the fluid. This causes friction.
Drag only happens to objects moving through the water.
Acceleration?
If a car exerts a bigger driving force (forwards) than the drag counter forces (backwards) the car will accelerate.
Deceleration?
If the driving force is less than the drag - the car will slow down.
Momentum??
This means how hard it is to stop it.
The greater the mass of an object the greater the momentum.
Momentum equation??
Momentum (kg m/s) = mass (kg) * velocity (m/s)
Equation for speed?
Speed (m/s) = distance travelled (m) / time taken (s)
