Topic 2 - Motion And Forces COPY Flashcards
What is a vector quantity?
Vectors have magnitude and direction
Give examples of vector quantities.(6)
Forces, velocity, displacement, weight, acceleration, momentum, etc.
What are scalar quantities?
Scalar quantities only have magnitude and no direction.
Give example of scalar quantities. (6)
Speed, distance, mass, energy, temperature, time, etc.
What is displacement?
Displacement is a vector quantity which measures the distance and the direction in a straight line form the starting point to the finishing point.
How is velocity different from speed?
Velocity is speed in a given direction.
What is the formula for average speed?
Average speed (m/s)= distance (m) / time (s)
What does the gradient of a distance-time graph represent?
Speed of an object.
Recall typical speeds of these:
- Wind
- Sound in air
- Person walking
- Person running
- Cyclist
- Car driving through town
- Car driving on Motorway
- Train
- Wind - 6m/s
- Sound in the air - 340m/s
- Person walking - 1 m/s
- Person running - 3 m/s
- Cyclist- 5.5 m/s
- Car driving through town - 13 m/s
- Car on Motorway - 30 m/s
- Train - 45 m/s
List two equations to work out acceleration.
Acceleration (m/s2)= (V - U) / T (Secs)
v2 - u2 = 2 X a (m/s2) X x(metre)
What does a diagonal line (/) represent on a distance-time graph?
Moving slowly/quickly (depending on the gradient) at a constant speed.
How do you calculate speed or distance on a point on a curved line on a distance-time graph?
Draw tangent to the curve at the point.
Then calculate the gradient of the tangent
What is uniform acceleration also known as?
Constant acceleration
What does a -acceleration mean?
Deceleration
What does the flat along 0 for the time axis mean (velocity-time graph)?
Stationary
How do you work out acceleration from a velocity-time graph?
Acceleration = Gradient of velocity-time graph
What does a diagonal line mean on a velocity-time graph?
Constant acceleration
Why does a object moving in a circular motion have a changing velocity?
- When an object moves in a circle at a constant speed, its direction constantly changes.
- A change in direction causes a change in velocity - This is because velocity is a vector quantity – it has an associated direction as well as a magnitude.
- A change in velocity results in acceleration, so an object moving in a circle is accelerating even though its speed may be constant.
Why must there be a centripetal force for circular motion?
- An object will only accelerate if a resultant force acts on it.
- For an object moving in a circle, this resultant force is the centripetal force that acts towards the middle of the circle.
Formula for weight (N)
Weight (N) = Mass (kg) x gravitational field strength (n/kg)
What is weight measured in?
Newtons
Describe the relationship between the weight of a body and the gravitational field strength
- Weight is the result of gravity. The gravitational field strength of the Earth is 10 N/kg (ten newtons per kilogram).
- This means an object with a mass of 1kg would be attracted towards the centre of the Earth by a force of 10N.
- We feel forces like this as weight.
What is Newton’s second law?
The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object.
This means that F = M x A
What is inertial mass?
The ratio of force over acceleration is called inertial mass.
Inertial mass is a measure of how difficult it is to change the velocity of an object.
What is Newton’s third law?
For every action, there is an equal and opposite reaction.
What is Newton’s first law?
If there is no forces acting on a body (or the forces acting on it are balanced) the object will continue to do what is it is already doing.
- if the object is stationary, it will remain
- if the object is moving, it will continue to move at the same speed and in the same direction
Describe the Core Practical : Investigate the relationship between force, mass and acceleration by varying the masses added to trolleys
- By releasing masses over the side of the bench a force will be applied to the trolley, causing it to accelerate down the ramp.
- Light gates can be positioned along the ramp to measure the velocity of the trolley at different points and record the time between these measurements.
- Different number of masses can be added to the trolley.
How do you find the distance travelled on a velocity-time graph?
Work out area under the line on the graph and above the horizontal axis.
How do you work out momentum?
Momentum (Kgm/s) = Mass (kg) x Velocity (m/s)
Which six factors affects stopping distance?
- Mass of Vehicle
- Speed of Vehicle
- Driver’s reaction time
- State of Vehicle’s brakes
- State of the road
- Amount of friction between tyre and road surface
How do you work out the stopping distance?
Thinking distance + Braking distance
What factors affect Driver’s reaction times?
- Age
- Gender
- Physical fitness
- Fatigue
- Distraction
- Alcohol
How do you work out force using momentum?
Force (N) = change in momentum (kgm/s) / time (s)
Estimate how the distance required for a road vehicle to stop in an emergency varies over a range of typical speeds
20 mph - 12m 30 mph - 23m 40 mph - 36m 50 mph - 53m 60 mph - 73m 70 mph - 96m
What does a flat line on a velocity-time graph represent?
Constant velocity
How does Newton’s third law connect to equilibrium situations?
- It applies in static (non-moving) situations, such as a book resting on a table.
- This is where the force from the weight of book and the reaction from the table is equal therefore cancelling out so it doesn’t move.
What is the acceleration in free fall?
10m/s2
How does Newton’a third law apply to car collisions?
- Newton’s Third Law of Motion applies in collisions, such as a car crashing into a tree.
- The car and tree exert equal and opposite forces on each other in the collision.
- When two objects collide the total momentum before the collision is equal to the total momentum in the absence of external forces.
- This is the law of conservation of momentum, it is true for all collisions.
What does a curved line going upwards represent?
Acceleration
How do you work out ‘Work Done’?
Work done = Energy transferred
Work (Joules) = Force (Newtons) x Distance moved in direction of force (metres)
What does a flat line on a distance-time graph represent?
Not moving/stationary
How do you work out ‘Kinetic Energy’?
Kinetic Energy = 1/2 x mass x velocity squared
What does Kinetic Energy equal when stopping a car?
KE = Work done
1/2 x mass x velocity squared = Force (applied by brakes) x Braking distance.
Why are large decelerations bad?
- When there is a car crash, the car, its contents and the passengers decelerate rapidly.
- They experience great forces because of the change in momentum which can cause injuries.
What safety features are implemented into cars to reduce injury from large decelerations?
Modern cars have safety features that absorb kinetic energy in collisions. These typically include:
- seat belts
- air bags
- crumple zones
How do safety features in a car prevent injury to the occupants?
- These features reduce injuries to the people in the car by absorbing energy from the impact.
- They increase the time taken for the change in momentum on the occupants’ bodies, and so reduce the forces involved and any subsequent injuries.
