2.5 Understanding the Effect of a Force

2.5 Understanding the Effect of a ForceChapter 2 Forces and MotionWhat is Force?A force is a push or a pull

Lifting objects

Pulling off the ring of a soft drink tin

Stretching a chest expander

Kicking a ball

Pressing a switchWhen you push or pull on an object, you need to know

The strength or magnitude of your force, andThe direction in which you are pushing and pulling.Thus, Force is a ________ quantity.VectorHow to measure a force?

A spring balance, which is used to measure the weight (or the gravitational pull of object) can be used to measure the magnitude of a force.The Effect of a Force1. A force can change the shape of an object. (deformation of an object).

Can change the shape of an object

A platicine is flattenedThe Effect of a Force

Can change the size of an object

A can is crushed.The Effect of a Force

A spring lengthens or compresses when you stretch or compress it.The Effect of a Force

A plastic ruler can be bent when a force exerted on it.The Effect of a ForceA force can change the original state of motion of an object.(from stationary to move / from moving state to stationary)

To move a stationary object.A pushing force is required to move a stalled carThe Effect of a Force

To stop a moving object

A goalkeeper stop the ballThe Effect of a Force

Can change the speed of a moving objectA ping-pong ball moves fasterThe Effect of a Force

Can change the direction of a moving object

A ping-pong ball changes its directionRelationship between acceleration , mass and force

Consider two identical speedboats A and B at rest on the sea.Different engine thrusts are applied to accelerate the boats.However, speedboat A which applies more engine thrust increases the velocity at higher rate.Mass, force, acceleration

Relationship between acceleration , mass and force

Consider two identical speedboats, P and Q with P heavily loaded. When the same engine thrust is applied, speedboat P accelerates slower than Q.Mass, force, acceleration

Experiment 2.2Relationship between acceleration and force applied on a constant mass.

Situation:

Figure (a) shows car A and car B of the same mass at the same starting line. Car B is a sport car.The engine capacity of sport car B is much bigger than car A. (a car with a bigger car capacity can provide greater engine thrust.)Figure (b) shows that sport car B has built up a higher velocity than car A after 3 seconds.Inference:____________________depends on __________________.

HypothesisWhen the mass of an object is constant, the greater ______________, the greater __________________.

Aim:To investigate the relationship between acceleration and the force applied on a constant mass.

Variables:Manipulated: __________________________________________________

Responding: __________________________________________________

Constant: __________________________________________________

Apparatus/Materials:Trolley, 3 identical elastic cords, runway, ticker-timer, carbonised ticker-tape, cellophane tape, 12 V a.c. power supply and a wooden block.Arrangements of apparatus:

Procedure:A friction-compensated inclined runway is prepared.The apparatus is then set up as shown in figure.The ticker-timer is switched on and the trolley is pulled down the runway by an elastic cord attached to the hind post of the trolley.The elastic cord is stretched until the other end is level with the front end of the trolley. The length is maintained as the trolley run down the runway.The ticker tape obtained is cut into strips of 10-tick. A tape chart is constructed and the acceleration, a, is determined.The experiment is repeated with 2, and 3 elastic cords to double and triple the pulling force to the same constant extension as when one elastic cord is stretched.

Result:(build your own ticker tape chart)Tabulation of data:(build a table to do comparisons)Conclusion:

Experiment 2.3Relationship between acceleration and mass of an object under a constant force

Situation:

Figure (a) shows two similar lorries, A and B in front of a traffic light. When the light turns green, both drivers step on the accelerator simultaneously with the same pressure to provide the same engine thrusts, F.Figure (b) shows that within 3 seconds, the empty lorry has built up a higher velocity than the heavy one.Inference:______________________ depends on _________________

HypothesisWhen the force applied on an object is constant, the greater __________________, the ____________________.

Aim:To investigate the relationship between acceleration and the mass of an object under a constant force

Variables:

Manipulated:______________________________

Responding: ______________________________

Constant: ________________________________

Apparatus/Materials:Ticker-timer, 12 V a.c power supply, 3 trolleys, elastic cord, runway, wooden block, ticker-tape and cellophane tape.Arrangements of apparatus:

Procedure:A friction-compensated inclined runway is prepared.The apparatus is then set up as shown in figure.The ticker-timer is attached to the trolley and passed through the ticker-timer.The ticker-timer is switched on and the trolley is pulled down the runway by an elastic cord attached to the hind post of the trolley.The elastic cord is stretched until the other end is level with the front end of the trolley. The length is maintained as the trolley run down the runway.The ticker tape obtained is cut into strips of 10-tick. A tape chart is constructed and the acceleration, a, is determined.The experiment is repeated using 2 trolleys (with a second trolley stacked on the first trolley) and 3 trolleys. The elastic cord is stretched to the same fixed length as in the first experiment.

Result:(build your own ticker tape chart)Tabulation of data:(build a table to do comparisons)Conclusion: