Forces And Motion Flashcards
What is the equation for average speed ?
Distance moved / time taken
What is the difference between speed and velocity
- Speed is how fast your going
* Velocity must also have the direction specified
What is the equation for acceleration ?
Change is velocity / time taken
What is acceleration?
- How quickly the velocity is changing
* Change in velocity can be a change in SPEED or DIRECTION or both
What is the weight equation ?
Mass x gravitational field strength
What are the different types of forces ?
- Gravity or weight
- Reaction force
- Electrostatic force
- Thrust (e.g. push and pull)
- Drag or Air resistance or Friction (slowing thing down)
- Lift (e.g. aeroplane wing)
- Tension (e.g. rope or cable)
What is Friction and Why is it there?
- Force that opposes motion
* There to slow things down
How does Friction occur?
- Between solid surfaces which are gripping
- Between solid surfaces which are sliding past each other
- Resistance/drag from fluids
How can you Reduce Friction between Solid Surfaces?
Put lubricant (oil/grease) between surfaces
How can Investigate the Motion of the Toy Car on a ramp?
- Set up ramp with car on top
- Measure distance between light gate (to find car average speed)
- When car goes through light gate, light broken, time recorded by data logging
- Repeat x10, get average time for car to reach light gate
What is the First Law?
Balanced forces mean no change in velocity
What is the Second Law?
A resultant force means acceleration
What forms can Acceleration be in?
- Starting
- Stopping
- Speeding up
- Slowing down
- Changing direction
Force=
Mass x Acceleration
What is the Third law?
If object A exerts a force on object B then object B exerts an equal and opposite force an object A
What are Examples of Vectors Quantities?
- Force
- Velocity
- Acceleration
- Momentum
What are Examples of Scalar Quantities?
- Mass
- Temperature
- Time
- Length
What are Vector Quantities?
Have size and direction
What are Scalar Quantities?
Have size and no direction
How can Objects reach a Terminal Velocity?
- First fall - more force accelerating it than resistance slowing it down
- Velocity Increases - resistance builds up
- Resistance reduces acceleration until resistance force equal to acceleration force
- Reached terminal velocity
What is Gravity?
Accelerating force acting on all falling objects
What does the Terminal Velocity of Falling Objects depend on?
- Determined by drag compared to weight
* Drag depends on its shape & area
What is an example using a Human Skydiver to explain why Terminal Velocity of Falling Objects is Dependant on their Shape and Area:
- No parachute - small area, force equal to weight pulling him down
- Terminal velocity - 120mph
- Parachute - more air resistance, same force pulling him down
- Terminal velocity - 15mph
What is Hooke’s Law?
Extension proportional to force
How can you Investigate Hooke’s Law with a Spring?
- Weighing stand, spring with hanging mass attached
- Measure length of spring
- Add one mass at a time, measure new length
- Extension - change in length from original length
- Repeat process x10
- Increase in mass = Increase In extension
How can Hooke’s Law Stop Working?
- Force great enough
- Force past elastic limit, material permanently stretched
- Force removed, material longer than at start
Stopping Distance =
Thinking Distance + Braking Distance
What Affects Thinking Distance?
- How fast your going
* Reaction time (drugs, tiredness, alcohol, inexperienced)
What Affects Braking Distance?
- How fast your going
- Mass of vehicle (larger mass-longer takes to stop)
- Quality of brakes
- Quality of grip - depends on road surface, weather, tyres
Momentum (kgm/s)=
Mass(Kg) x Velocity (m/s)
Momentum Before =
Momentum After
What happens when a Force acts on a object?
- Causes change in momentum
* Larger force = faster change
Force (N) =
Change in momentum (kgm/s) / time(s)
How do Crumple Zones Reduce an Accident?
- Crumple on impact
* Increasing time taken for car to stop
How do Seat Belts Reduce an Accident?
- Stretch slightly
- Increasing time taken for wearer to stop
- Reduces forces acting on chest
How do Air Bags Reduce an Accident?
Slows you down more gradually
Moment (Nm) =
Force (N) x perpendicular distance (m) between line of action and pivot
What is a Moment?
Turning effect of a force
How to get a Maximum Moment on Spanner?
Push at right angles (perpendicular) to spanner
How do you get a Larger Moment on a Spanner?
- Larger force
* Longer spanner - distance from pivot is greater
What is the Centre of Gravity?
- Point through which weight of a body acts
* Object swing until centre of gravity vertically below point of suspension
How can you find the Centre of Gravity of a Flat Shape?
- Suspend shape & plumb line at same point,wait until not moving
- Draw line along plumb line
- Do same thing again, but suspend shape from different pivot point
- Centre is Gravity = 2 lines cross
What does the Principle of Moments say?
If an object is balanced then : Total anticlockwise moments = total clockwise moments
Why are Forces Not always Equal across all supports?
- Light rod - supported at both ends, upwards force by each support won’t always be same
- Heavy object - placed on rod, support closest to object will provide larger force
What does it mean if Moments are Not Equal?
There will be a resultant moment - object turn
